Methods for fiber reinforced additive manufacturing

ABSTRACT

Various embodiments related to three dimensional printers, and reinforced filaments, and their methods of use are described. In one embodiment, a void free reinforced filament is fed into an extrusion nozzle. The reinforced filament includes a core, which may be continuous or semi-continuous, and a matrix material surrounding the core. The reinforced filament is heated to a temperature greater than a melting temperature of the matrix material and less than a melting temperature of the core prior to extruding the filament from the extrusion nozzle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/055,483, filed Aug. 6, 2018, which is a continuation of U.S. patentapplication Ser. No. 15/186,651 [now U.S. Pat. No. 10,040,252], filedJun. 20, 2016, which is a continuation of U.S. patent application Ser.No. 14/297,437 [now U.S. Pat. No. 9,370,896], filed Jun. 5, 2014. TheSer. No. 14/297,437 application is a continuation-in-part of U.S. patentapplication Ser. No. 14/222,318 [now Abandoned], filed Mar. 21, 2014.The Ser. No. 14/222,318 application claims the benefit under 35 U.S.C. §119(e) of U.S. provisional application Ser. No. 61/831,600 [Expired]filed Jun. 5, 2013, U.S. provisional application Ser. No. 61/815,531[Expired] filed Apr. 24, 2013, U.S. provisional application Ser. No.61/804,235 [Expired] filed Mar. 22, 2013, U.S. provisional applicationSer. No. 61/878,029 [Expired] filed Sep. 15, 2013, U.S. provisionalapplication Ser. No. 61/881,946 [Expired] filed Sep. 24, 2013, U.S.provisional application Ser. No. 61/847,113 [Expired] filed Jul. 17,2013, U.S. provisional application Ser. No. 61/902,256 [Expired] filedNov. 10, 2013, U.S. provisional application Ser. No. 61/880,129[Expired] filed Sep. 19, 2013, U.S. provisional application Ser. No.61/883,440 [Expired] filed Sep. 27, 2013, and U.S. provisionalapplication Ser. No. 61/907,431 [Expired] filed Nov. 22, 2013. The Ser.No. 14/297,437 application also claims the benefit under 35 U.S.C. §119(e) of U.S. provisional application Ser. No. 61/831,600 filed Jun. 5,2013, U.S. provisional application Ser. No. 61/847,113 filed Jul. 17,2013, U.S. provisional application Ser. No. 61/878,029 filed Sep. 15,2013, U.S. provisional application Ser. No. 61/881,946 filed Sep. 24,2013, and U.S. provisional application Ser. No. 61/902,256 filed Nov.10, 2013. Each disclosure referenced above is herein incorporated byreference in its entirety.

FIELD

Aspects relate to three dimensional printing.

BACKGROUND

“Three dimensional printing” as an art includes various methods such asStereolithography (SLA) and Fused Filament Fabrication (FFF). SLAproduces high-resolution parts, typically not durable or UV-stable, andis used for proof-of-concept work; while FFF extrudes through a nozzlesuccessive filament beads of ABS or a similar polymer.

“Composite Lay-up” is not conventionally related to three dimensionalprinting. In this art, preimpregnated (“prepreg”) composite sheets offabric are impregnated with a resin binder into two-dimensionalpatterns. One or more of the individual sheets are then layered into amold and heated to liquefy the binding resin and cure the final part.

“Composite Filament Winding” is also not conventionally related to threedimensional printing. In this art, sticky “tows” including multiplethousands of individual carbon strands are wound around a custom mandrelto form a rotationally symmetric part. Filament winding is typicallylimited to convex shapes due to the taut filaments “bridging” anyconcave shape.

There is no commercial or experimental three dimensional “printing”technique which provides the benefits of composite lay-up, or compositefilament winding.

SUMMARY

According to a first version of the present invention, one combinationof steps for additive manufacturing of a part includes supplying anunmelted void free fiber reinforced composite filament including one ormore axial fiber strands extending within a matrix material of thefilament, having no substantial air gaps within the matrix material. Theunmelted composite filament is fed at a feed rate along a clearance fitzone that prevents buckling of the filament until the filament reaches abuckling section (i.e., at a terminal and of the nozzlet, opposing thepart, optionally with a clearance between the nozzlet end and the partof a filament diameter or less) of the nozzlet. The filament is heatedto a temperature greater than a melting temperature of the matrixmaterial to melt the matrix material interstitially within the filament,in particular in a transverse pressure zone. A ironing force is appliedto the melted matrix material and the one or more axial fiber strands ofthe fiber reinforced composite filament with an ironing lip as the fiberreinforced composite filament is deposited in bonded ranks to the part.In this case, the ironing lip is translated adjacent to the part at aprinting rate that maintains a neutral to positive tension in the fiberreinforced composite filament between the ironing lip and the part, thisneutral-to-positive (i.e., from no tension to some tension) tensionbeing less than that necessary to separate a bonded rank from the part.

According to a second version of the present invention, anotheradditional or alternative combination of steps for additivemanufacturing of a part includes the above-mentioned supplying step, andfeeding the fiber reinforced composite filament at a feed rate. Thefilament is similarly heated, in particular in a transverse pressurezone. The melted matrix material and the at least one axial fiber strandof the composite filament are threaded (e.g., through a heated printhead, and in an unmelted state) to contact the part in a transversepressure zone. This transverse pressure zone is translated relative toand adjacent to the part at a printing rate to bring an end of thefilament (including the fiber and the matrix) to a melting position. Theend of the filament may optionally buckle or bend to reach thisposition. At the melting position, the matrix material is meltedinterstitially within the filament.

According to a third version of the present invention, athree-dimensional printer for additive manufacturing of a part includesa fiber composite filament supply (e.g., a spool of filament, or amagazine of discrete filament segments) of unmelted void free fiberreinforced composite filament including one or more axial fiber strandsextending within a matrix material of the filament, having nosubstantial air gaps within the matrix material. One or more linear feedmechanisms (e.g., a driven frictional rollers or conveyors, a feedingtrack, gravity, hydraulic or other pressure, etc., optionally withincluded slip clutch or one-way bearing to permit speed differentialbetween material feed speed and printing speed) advances unmeltedcomposite filament a feed rate, optionally along a clearance fit channel(e.g., a tube, a conduit, guide a channel within a solid part, conveyorrollers or balls) which guides the filament along a path or trajectoryand/or prevents buckling of the filament. A print head may include (alloptional and/or alternatives) elements of a heater and/or hot zoneand/or hot cavity, one or more filament guides, a cold feed zone and/orcooler, and/or a reshaping lip, pressing tip, ironing tip, and/orironing plate, and/or linear and/or rotational actuators to move theprint head in any of X, Y, Z, directions and/or additionally in one tothree rotational degrees of freedom. A build platen may include a buildsurface, and may include one or more linear actuators to move the buildplaten in any of X, Y, Z, directions and/or additionally in one to threerotational degrees of freedom. The heater (e.g., a radiant heater, aninductive heater, a hot air jet or fluid jet, a resistance heater,application of beamed or radiant electromagnetic radiation, optionallyheating the ironing tip) heats the filament, and in particular thematrix material, to a temperature greater than a melting temperature ofthe matrix material (to melt the matrix material around a single fiber,or in the case of multiple strands, interstitially among the strandswithin the filament). The linear actuators and/or rotational actuatorsof the print head and/or build platen may each solely and/or incooperation define a printing rate, which is the velocity at which abonded rank is formed. A controller optionally monitors the temperatureof the heater, of the filament, and/or and energy consumed by the heatervia sensors.

In this third version of the invention and optionally other versions ofthe invention, the feed mechanism, clearance fit channel, linear orrotational actuators of the build platen and/or the linear androtational actuators, guides, hot cavity, and/or reshaping or ironinglip or tip of the print head may optionally cooperate (any combinationor permutation thereof or all) as a transverse pressure zone thatpresses and/or melts filaments onto the build platen or into the partbeing printed. Optionally, the linear and rotational actuators of theprint head and/or build platen, and/or one or more linear feedmechanisms may be controlled by a controller monitoring force,displacement, and/or velocity sensors to apply a compressive force alongthe axial strands (e.g., tangentially to a feed roller diameter) of thefilament and/or apply a reaction force from the build platen or partbeing printed to press melted matrix filaments against the build platenor against or into previous layers of the part to form bonded ranks(i.e., substantially rectangular ranks adhered to substantially flatsurfaces below and to one side thereof). Fully optionally in addition orthe alternative, the linear and rotational actuators of the print headand/or build platen, and/or one or more linear feed mechanisms may becontrolled by a controller monitoring force, displacement, and/orvelocity sensors to apply a transverse, sideways, downwards, ironingand/or ironing force (optionally using a surface of or adjacent theprint head, which may be a reshaping and/or ironing lip, tip, or plate)to the side of the melted matrix filament to press and/or iron themelted matrix filaments against the build platen or against or intoprevious layers of the part to form bonded ranks. Fully optionally inaddition or the alternative, the linear and rotational actuators of theprint head and/or build platen, and/or one or more linear feedmechanisms may be controlled by a controller monitoring force,displacement, and/or velocity sensors to apply a neutral to positivetension force through the strand and unmelted matrix of the filamentand/or between the build platen, previously deposited bonded ranks andthe print head or feeding mechanism(s) (optionally using a surface of oradjacent the print head, which may be a reshaping and/or ironing lip,tip, or plate, and further optionally using interior surfaces of theprint head or guides, and/or feeding mechanism clutches, slips, motordrive, idling, motor internal resistance, and/or small resistancecurrents) adjacent to the part at a printing rate that maintains neutralto positive tension in the fiber reinforced composite filament betweenthe reshaping lip and the part. This tension force is optionally aneutral to positive tension force less than that necessary to separate abonded rank from the part for sustained formation of bonded ranks, andfurther optionally and/or in the alternative, may be sufficient toseparate or sever a filament with a discontinuous internal fiberconnected by melted matrix to the print head.

In this third version of the invention and optionally the first andsecond and other versions of the invention, the linear and rotationalactuators of the print head and/or build platen, and/or one or morelinear feed mechanisms may be controlled by a controller monitoringforce, displacement, and/or velocity sensors to apply a transverse,sideways, downwards, reshaping and/or ironing force (optionally using asurface of or adjacent the print head, which may be a reshaping and/orironing lip, tip, or plate) to generate a different balance of forceswithin the printer, filament, and part in different printing phases(e.g., threading phases versus printing phases). For example, in oneversion of the invention, the linear and rotational actuators of theprint head and/or build platen, and/or one or more linear feedmechanisms may be controlled by a controller monitoring force,displacement, and/or velocity sensors to apply a transverse, sideways,downwards, reshaping and/or ironing force (optionally using a surface ofor adjacent the print head, which may be a reshaping and/or ironing lip,tip, or plate) may apply bonded ranks primarily via lateral pressing andaxial tension in a continuous printing phase of applying bonded ranks,and primarily via lateral pressing and axial compression in a threadingor initialization phase.

None of the abovementioned steps or structures in the first throughthird versions or other versions are critical to the invention, and theinvention can be expressed as different combinations of these. Inparticular, pressing a fiber reinforced filament into a part mayoptionally be temporarily performed during threading or initializationby axial compression along the fiber composite (unmelted fiberstrand(s), partially melted and partially glass matrix), and/or by“ironing” and/or reshaping in the transverse pressure zone (e.g., printhead tip) and/or by the reshaping lip and/or by a companion “ironing”plate following the printhead. Each approach and structure is effectivein itself, and in the invention is considered in permutations andcombinations thereof. Further, the pressing may be done in combinationwith compression or tension maintained in the filament via the unmeltedfiber strands. Pressing or ironing may be done in the presence oftension upstream and downstream of the transverse pressure zone (e.g.,print head tip) and/or the ironing lip and/or companion “ironing” plate,but also or alternatively in the presence of tension downstream of thepressing and also upstream of the transverse pressure zone (e.g., printhead tip) and/or ironing lip and/or by companion “ironing” plate.

In each of these first through third versions, as well as other versionsof the invention, optionally the matrix material comprises athermoplastic resin having an unmelted elastic modulus of approximately0.1 through 5 GPa and/or unmelted ultimate tensile strength ofapproximately 10 through 100 MPa, and a melted elastic modulus of lessthan 0.1 GPa and melted ultimate tensile strength of less than 10 MPa,and the one or more axial fiber strands have an elastic modulus ofapproximately 5-1000 GPa and an ultimate tensile strength ofapproximately 200-100000 MPa. These versions may optionally maintain asubstantially constant cross sectional area of the fiber reinforcedcomposite filament in clearance fit zone, the non-contact zone, thetransverse pressure zone, and as a bonded rank is attached to theworkpiece. In each of these first through third versions, optionally thefilament has a cross sectional area greater than 1×10E-5 inches and lessthan 2×10E-3 inches. Further optionally, the at least one axial strandincludes, in any cross-sectional area, between 100 and 6000 overlappingaxial strands or parallel continuous axial strands. Such matrixmaterials include acrylonitrile butadiene styrene, epoxy, vinyl, nylon,polyetherimide, polyether ether ketone, polyactic acid, or liquidcrystal polymer, and such axial strand materials include carbon fibers,aramid fibers, or fiberglass.

In each of these first through third versions, as well as other versionsof the invention, at least one of the feed rate and the printing rateare optionally controlled to maintain compression in the fiberreinforced composite filament within the clearance fit zone.Additionally or in the alternative for these and other versions,optionally in a threading or initialization phase, the filament isheated in an non-contact zone immediately upstream of the ironing, andthe feed and printing rates controlled to induce axial compression alongthe filament within the non-contact zone primarily via axial compressiveforce within the one or more axial fiber strands extending along thefilament. Additionally or in the alternative for these and otherversions, optionally in a threading or initialization phase, at leastone of the feed rate and the printing rate are controlled to compressthe fiber reinforced composite filament and translate an end of thefilament abutting the part laterally underneath an ironing lip to beironed by application of heat and pressure. Additionally or in thealternative for these and other versions, the filament is heated and/ormelted by the ironing lip, and one or both of the feed rate and theprinting rate are controlled to maintain neutral to positive tension inthe fiber reinforced composite filament between the ironing lip and thepart primarily via tensile force within the at least one axial fiberstrand extending along the filament.

In each of these first through third versions, as well as other versionsof the invention, the unmelted fiber reinforced filament is optionallycut by a cutter at or adjacent the clearance fit zone; and/or cut by acutter core at or adjacent one or both of the clearance fit zone or theironing lip. Additionally or in the alternative for these and otherversions, the clearance fit zone includes at least one channel forming aclearance fit about the fiber reinforced composite filament, and thefiber reinforced composite is maintained at a temperature below a glasstransition temperature of the matrix material throughout the at leastone channel. Supplying is optionally via a cartridge to decouple thespeed of manufacturing or forming the reinforced fiber material (e.g.,combining the fiber with the matrix) from the speed of printing.

In each of these first through third versions, as well as other versionsof the invention, height of the ironing lip from the current printinglayer surface (e.g., bonded rank layer below, either FFF or fibercomposite, or platen) is optionally controlled to be less than thediameter of the filament (e.g., the height of each bonded rank is lessthan the diameter of the filament). Pressing or ironing the filament ina transverse pressure zone may include applying a ironing force to thefilament with as the filament is deposited in bonded ranks. Additionallyor in the alternative for these and other versions, the method includespreventing the filament from touching a heated wall of a cavity definingthe non-contact zone; and/or includes touching the filament to a heatedironing lip in the transverse pressure zone to melt matrix material ofthe filament.

In each of these first through third versions, as well as other versionsof the invention, the method optionally further includes, as the meltedmatrix material and the axial fiber strand(s) are pressed into the partin the transverse pressure zone to form laterally and vertically bondedranks, flattening the bonded ranks on at least two sides by applying afirst ironing force to the melted matrix material and the at least oneaxial fiber strand with the ironing lip, and applying a opposingreshaping force to the melted matrix material and the at least one axialfiber strand as a normal reaction force from the part itself.

In each of these first through third versions, as well as other versionsof the invention, the method may further include drawing the fiberreinforced composite filament in the transverse pressure zone from aconnection to a first portion of the part, translating the transversepressure zone through free space; and ironing to reconnect the fiberreinforced composite filament to a second portion of the part.

In each of these first through third versions, as well as other versionsof the invention, the method may include forming a solid shell with thefilament; and/or the ironing lip may be rounded. Additionally or in thealternative for these and other versions, the ironing lip may be at thetip of a nozzlet or printing guide with a cross- sectional area of thenozzlet outlet larger than a cross-sectional area of the nozzlet orprinting guide inlet. Additionally or in the alternative for these andother versions, the cross sectional area within the walls of a heatingcavity or non-contact zone is larger than a cross-sectional area of theclearance fit zone.

In each of these first through third versions, as well as other versionsof the invention, the method may include depositing bonded ranks in afirst direction in a first portion of a part and in a second directionin a second portion of the part. Additionally or in the alternative forthese and other versions, the method may include pulling the filamentout of a nozzlet or printing guide when a dragging force applied to thefilament is greater than a force threshold of an associated feedingmechanism.

In each of these first through third versions, as well as other versionsof the invention, the one or more fiber cores may be constructed as atrain of separate segments extending in an axial direction of thefilament. In this case, the segments may be located at pre-indexedlocations along the axial direction of the filament; and/or at leastsome of the segments may overlap along the axial direction of thefilament. Additionally or in the alternative for these and otherversions, the average length of the segments may be less than or equalto a length of the heated or non-contact zone.

In each of these first through third versions, as well as other versionsof the invention, the push-pultrusion process of depositing a firstfilament into a layer of matrix material in a first desired pattern maybe followed by or performed in parallel with curing a matrix layer(e.g., stereolithography or selective laser sintering) to form a layerof a part including the deposited first filament. Additionally or in thealternative for these and other versions, this alternative mayoptionally include cutting the first filament and depositing a secondfilament in a second desired pattern in the layer of matrix material.

One aspect of the present invention prints structures using asubstantially void-free preimpregnated (prepreg) material that remainsvoid-free throughout the printing process. One form of this material isa reinforced filament including a core with multiple continuous strandspreimpregnated with a thermoplastic resin that has already been “wicked”into the strands, and applied using one of the push-pultrusionapproaches of the present invention to form a three dimensionalstructure. A composite formed of thermoplastic (or uncured thermoset)resin having wetted or wicked strands, may not be “green” and is alsorigid, low-friction, and substantially void free. Another form mayemploy a single, solid continuous core. Still another form may use asectioned continuous core, i.e., a continuous core sectioned into aplurality of portions along the length is also contemplated. Stillanother form may employ a solid core or multiple individual strands thatare either evenly spaced from one another or include overlaps. “Voidfree” as used herein with respect to a printing material may mean, at anupper limit, a void percentage between 1% than 5%, and at a lower limit0%, and with respect to a printed part, at an upper limit, a voidpercentage between 1 and 13%, and at a lower limit 0%. Optionally, thepush-pultrusion process may be performed under a vacuum to furtherreduce or eliminate voids.

A fiber or core “reinforced” material is described herein. The fiber orcore may either be positioned within an interior of the filament or thecore material may extend to an exterior surface of the filament, or formultistrand implementations, both. The term including “reinforced” mayoptionally extend to strands, fibers, or cores which do not provideexceptional reinforcing structural strength to the composite, such asoptical fibers or fluid conducting materials, as well as conductivematerials. Additionally, it should be understood that a core reinforcedmaterial also includes functional reinforcements provided by materialssuch as optical fibers, fluid conducting channels or tubes, electricallyconductive wires or strands.

The present invention contemplates that optionally, the entire processof push-pultrusion, including the use of different compatible materialsherein, many be a precursor or a parallel process other modes ofadditive manufacturing, in particular stereolithography (SLA), selectivelaser sintering (SLS), or otherwise using a matrix in liquid or powderform. Push-pultrusion may embed within or about parts made by these modesubstantially void free parts, enabling the entire part to exhibitenhanced strength.

If the push-pultrusion process is used to lay down bonded ranks with adominant direction or directions, these directions may optionallyexhibit anisotropic strength both locally and overall. Directionality oranisotropy of reinforcement within a structure can optionally provideenhanced part strength in desired locations and directions to meetspecific design requirements or enable lighter and/or stronger parts.

Optionally in any above-described invention, a cutter may provideselective deposit of a desired length of composite filament and/orbonded rank. The cutter is optionally located between a feedingmechanism for the core material and the outlet of a nozzlet. Anadditional or alternative cutter may be placed at the nozzlet's outlet.Alternatively or in addition, and optionally in any above-describedinvention, the substantially void free material may be fed through ashaping nozzlet to provide a desired shape, especially flattening. Thenozzlet may include an ironing lip that includes a shape for forming topor side surfaces of bonded ranks, in particular a curved lip or chamfer,a straight lip or chamfer, or a square or rectangle reshaping surface.

Optionally in any above-described invention, the matrix material may beacrylonitrile butadiene styrene (ABS), epoxy, vinyl, nylon,polyetherimide (PEI), Polyether ether ketone (PEEK), Polyactic Acid(PLA), or Liquid Crystal Polymer. The core or strands of the core mayreinforce structurally, conductively (electrically and/or thermally),insulatively (electrically and/or thermally), optically and/or in amanner to provide fluidic transport. The core or strands of the core mayinclude, in particular for structural reinforcing, carbon fiber, aramidor high strength nylon fiber, fiberglass. Further, multiple types ofcontinuous cores or strands may be combined in a single continuous corereinforced filament to provide multiple functionalities such as bothelectrical and optical properties.

Optionally in any above-described invention or versions of theinvention, fiber reinforced composite filaments with different resin tofiber ratios may provide different properties within different sectionsof the part, e.g., printed with different printheads at differentstages. Similarly optionally, a “low-resin” fiber reinforced compositefilament skeletal filler may be used for the internal construction tomaximize the strength-to-weight ratio (e.g., 30% resin/70% fiber bycross sectional area). “Low-resin” means a resin percentage in crosssectional area from 30% to 50%. Similarly optionally a “High-resin”fiber reinforced composite filament shell coating (e.g., 90% resin/10%fiber by cross sectional area) may be used to prevent the possible printthrough of an underlying core or individual fiber strand of the core.Additionally, in some embodiments and versions of the invention, theconsumable material may have zero fiber content, and be exclusivelyresin and/or printed with conventional FFF.

Optionally in any above-described invention or versions of theinvention, the unmelted composite filament is fed at a feed rate along aclearance fit zone that prevents buckling of the filament until saidfilament reaches the buckling section of the nozzlet (outlet).

All of the listed options apply individually, and in any operablepermutation or combination to each of the first, second, third, andother versions of the invention, including that acts or steps areimplemented with apparatus structures disclosed herein as would beunderstood by one of skill in the art, and apparatus structures performacts or steps as disclosed herein as would be understood by one of skillin the art. In all cases throughout the invention, the term “may”denotes an optional addition or alternative material, structure, act, orinvention to the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are schematic representations of a three dimensionalprinting system using a continuous core reinforced filament;

FIG. 2 is a representative flow chart of a three dimensional printingprocess;

FIGS. 3A-3D are schematic representations of various embodiments of coreconfigurations of a continuous core reinforced filament 2;

FIG. 4 is a schematic representation of a core configuration of acontinuous core reinforced filament with secondary functional strands.

FIG. 5 is a schematic representation of fiber bunching within ahypothetical converging nozzle;

FIG. 6A-6C are a schematic representations of nozzlets utilized in someembodiments of the printing system;

FIG. 7 is a schematic representation of a three dimensional printingsystem;

FIG. 8 is a schematic representation of a three dimensional printingsystem including a cutter and a printing process bridging an open space;

FIG. 9 is a schematic representation of a part formed by thethree-dimensional printing system and/or process that includes anenclosed open space;

FIG. 10 is a schematic representation of a three-dimensional printingsystem including a guide tube;

FIG. 11 is a photograph of a three dimensional printing system includinga guide tube;

FIGS. 12A and 12B are is a schematic representations of a shear cuttinghead in respective first and second indexing positions;

FIG. 13 is a schematic representation of a multi-nozzlet print headincluding shear cutting;

FIGS. 14A-14C are a schematic representations of nozzles and roundedoutlet nozzles respectively;

FIG. 15A is a schematic cross-sectional view of a cutter integrated witha nozzlet tip;

FIG. 15B is a schematic cross-sectional view of the cutter integratedwith a nozzlet tip depicted in FIG. 14A rotated 90°;

FIG. 15C-15D are bottom views an embodiment of a cutter integrated witha nozzlet tip;

FIG. 16 is a schematic cross-sectional view of a cutter integrated witha nozzlet tip;

FIG. 17A is a schematic representation of a three-dimensional printingsystem applying a compaction pressure during part formation;

FIG. 17B is a schematic representation of a continuous core reinforcedfilament to be utilized with the printing system prior to deposition;

FIG. 17C is a schematic representation of the continuous core reinforcedfilament and surrounding beads of materials after deposition usingcompaction pressure;

FIG. 18A is a schematic representation of a prior art nozzle;

FIG. 18B is a schematic representation of a divergent nozzle;

FIG. 18C is a schematic representation of the divergent nozzlet of FIG.18B shown in a feed forward cleaning cycle;

FIG. 19A is a schematic representation of a continuous core filamentbeing printed with a straight nozzle;

FIG. 19B is a schematic representation of a green towpreg being printedwith a straight nozzle;

FIGS. 19C-19E are schematic representations of a continuous corefilament being threaded and printed with a divergent nozzle;

FIG. 20A is a schematic representation of a multi-material nozzlet witha low friction cold feeding zone;

FIG. 20B is a schematic representation of a slightly convergent nozzletincluding a low friction cold feeding zone;

FIG. 21A is a schematic representation of a prior art nozzle;

FIGS. 21B-21D represent various embodiments of nozzle geometries;

FIG. 22 is a schematic representation of an anti-drip nozzle andpressure reduction system;

FIG. 23A is a schematic representation of a semi-continuous corefilament positioned within a nozzle;

FIG. 23B is a schematic representation of a semi-continuous corefilament with overlapping strands positioned within a nozzle;

FIG. 23C is a schematic representation of a semi-continuous corefilament with aligned strands and positioned within a nozzle;

FIG. 24A is a schematic representation of a multifilament continuouscore;

FIG. 24B is a schematic representation of a semi-continuous corefilament with offset strands;

FIG. 24C is a schematic representation of a semi-continuous corefilament with aligned strands;

FIG. 24D is a schematic representation of a semi-continuous corefilament with aligned strands and one or more continuous strands;

FIG. 25 is a schematic representation of a fill pattern using asemi-continuous core filament;

FIG. 26 is a schematic representation of multiple printed layers formedby the three-dimensional printing system and/or process with thedifferent layers and different portions of the layers includingdifferent fiber directions;

FIG. 27A is a schematic representation of a three dimensional printingprocess for forming a component in a first orientation;

FIG. 27B is a schematic representation of a fixture to use with the partof FIG. 27A;

FIG. 27C is a schematic representation of a three dimensional printingprocess for forming a component on the part of FIG. 27A in a secondorientation;

FIG. 28A is a schematic representation of a three dimensional printingprocess using a multiaxis system in a first orientation;

FIG. 28B is a schematic representation of forming a component in anotherorientation on the part of FIG. 28A;

FIG. 29 is a schematic representation of a three dimensional printingsystem using a continuous core reinforced filament;

FIG. 30A is a schematic representation of a part including a shellapplied to the sides using a three dimensional printing process;

FIG. 30B is a schematic representation of a part including a shellapplied to the top and sides using a three-dimensional printing process;

FIG. 30C is a schematic representation of a part including a shell thathas been offset from an underlying supporting surface;

FIG. 30D is a schematic representation of a part formed with a fillmaterial;

FIG. 30E is a schematic representation of a part formed with compositematerial extending inwards from the corners and polymer fill in theinterior;

FIG. 30F is a schematic representation of a part formed with compositematerial extending inwards from the corners and polymer fill in theinterior;

FIG. 30G is a schematic representation of a part formed with compositematerial extending inwards from the corners and polymer fill in theinterior;

FIG. 31A is a schematic representation of an airfoil formed withdiscrete subsections including fiber orientations in the same direction;

FIG. 31B is a schematic representation of an airfoil formed withdiscrete subsections including fiber orientations in differentdirections;

FIG. 31C is a schematic representation of an airfoil formed withdiscrete subsections and a shell formed thereon;

FIG. 32 is a schematic representation of a three dimensional printingsystem including a print arm and selectable printer heads;

FIG. 33 is a schematic representation of a multi-element printer headfor use in the printing system;

FIG. 34 is a schematic representation of a stereolithography threedimensional printing process including deposited reinforcing fibers; and

FIG. 35 is a schematic representation of a stereolithography threedimensional printing process including deposited reinforcing fibers.

DETAILED DESCRIPTION

In both of the relatively recent arts of additive manufacturing andcomposite lay-up, coined words have become common. For example, a“prepreg” is a pre-impregnated composite material in which a resinmatrix and a fiber assembly are prepared ahead of time as a compositeraw material. A “towpreg” is “prepreg” formed from a combination of a“tow” (a bundle of hundreds to thousands of fiber strands at very highfiber percentage, e.g., 95%) and a sticky (at room temperature) resin,conventionally being dominated by the fibers of the impregnated tow(e.g., 75% fiber strands), with the sticky resin being impregnated as ameans of transferring shear between fiber strands roughly adjacent in afilament winding process and sticking the towpreg to the rotated member.“Pultrusion” is one of the processes of making a towpreg, where a tow ispulled through a resin to form—in a process conducted entirely intension—elongated and typically hardened composites including the towembedded in the resin.

As used herein, “extrusion” shall have its conventional meaning, e.g., aprocess in which a stock material is pressed through a die to take on aspecific shape of a lower cross-sectional area than the stock material.Fused Filament Fabrication (FFF) is an extrusion process. Similarly,“nozzle” shall have its conventional meaning, e.g., a device designed tocontrol the direction or characteristics of a fluid flow, especially toincrease velocity and/or restrict cross-sectional area, as the fluidflow exits (or enters) an enclosed chamber.

In contrast, the present invention shall use the coined word“push-pultrusion” to describe the overall novel process according to theinvention, in which unlike extrusion, forward motion of the fiberreinforced composite printing material includes a starting, threading,or initialization phase of compression followed by tension of embeddedfiber strands, as well as melted/cured and unmelted/uncured states ofthe matrix throughout the printhead as the printing material formsbonded ranks on a build table, and successively within a part. Thepresent invention shall also use the coined word “nozzlet” to describe aterminal printing head according to the invention, in which unlike a FFFnozzle, there is no significant back pressure, or additional velocitycreated in the printing material, and the cross sectional area of theprinting material, including the matrix and the embedded fiber(s),remains substantially similar throughout the process (even as depositedin bonded ranks to the part).

The present invention shall also use the coined word “push-pulpreg” todescribe a material useful in push-pultrusion, which—in contrast to aconventional towpreg—the resin is preferably a thermoplastic that (i)provides sufficient friction and exposed resin material to be fed byrollers or other friction feed (ii) is sufficiently stiff (i.e., normalunmelted elastic modulus) to be pushed through a clearance fit tube orchannel without buckling in an unmelted, “glass” state, the stiffnessprovided by the embedded fiber strands and to a lesser extent theunmelted matrix resin (iii) and/or has no appreciable “tack”/moleculardiffusion in ambient conditions, i.e., is in a “glass” state in ambientor even warmed conditions so that it can be readily pushed through sucha tube without sticking.

Consolidation is typically advantageous to remove voids that result fromthe inability of the resin to fully displace air from the fiber bundle,tow, or roving during the processes that have been used to impregnatethe fibers with resin. The individually impregnated roving yarns, tows,plies, or layers of prepregs are usually consolidated by heat andpressure by compacting in an autoclave. The consolidation step hasgenerally required the application of very high pressures and hightemperatures under vacuum for relatively long times. Furthermore, theconsolidation process step using an autoclave or oven requires a“bagging” operation to provide the lay-up with a sealed membrane overthe tool to allow a vacuum to be applied for removal of air and toprovide the pressure differential necessary to effect consolidation inthe autoclave. This process step further reduces the total productivityof the composite part operation. Thus, for a thermoplastic composite itwould be advantageous to in-situ consolidate to a low void compositewhile laminating the tape to the substrate with the ATL/AFP machine.This process is typically referred to as in-situ ATL/AFP and thematerial used in that process called an in-situ grade tape.

Lastly, in the three-dimensional printing art, “filament” typicallyrefers to the entire cross-sectional area of a spooled build material,while in the composites art, “filament” refers to individual fibers of,for example, carbon fiber (in which, for example, a “1K tow” will have1000 individual strands). For the purposes of the present invention,“filament” shall retain the meaning from three-dimensional printing, and“strand” shall mean individual fibers that are, for example, embedded ina matrix, together forming an entire composite “filament”.

Additive manufacturing methods often result in reduced the strength anddurability versus conventional molding methods. For example, FusedFilament Fabrication results in a part exhibiting a lower strength thana comparable injection molded part, due to weaker bonding between theadjoining strips (e.g., “bonded ranks”) of deposited material (as wellas air pockets and voids.

Prepreg sheet composite construction method are time consuming anddifficult, and thereby expensive. Further, bending prepreg sheets aroundcurves may cause the fibers to overlap, buckle, and/or distort resultingin undesirable soft spots.

Feeding a commercial fiber “Towpreg” through a plastic bath to addmatrix resin, then further feeding through a custom print head does notresult in a viable additive process, due to the extremely flexible andhigh-friction (sticky) construction. Moreover, this process binds thespeed of manufacturing this composite to the speed of printing it (evenwere printing viable). Towpreg typically requires, and is sold withappropriate “tack” (a level of room-temperature adhesion sufficient tomaintain the position of the tow after it has been deposited on a toolor lay-up). Further, towpreg “green” materials tend to entrap air andinclude air voids, which are only removed by high tension and/or asubsequent vacuum and/or heating steps. These steps also slow down theprinting process.

Accordingly, there is a need for composite additive manufacturing thatis faster than lay-up or winding; that reduces or prevents entrapped airin the bonded ranks, avoiding most vacuum or heating post-processes;that provides an ability to deposit composite material in concaveshapes, and/or construct discrete features on a surface or compositeshell.

Turning now to the figures, specific embodiments of the disclosedmaterials and three dimensional printing processes are described.

FIG. 1A depicts an embodiment of a three dimensional printer 3000 inbefore applying a fiber reinforced composite filament 2 to build astructure. The fiber reinforced composite filament 2 (also referred toherein as continuous core reinforced filament) may be a push-pulpregthat is substantially void free and includes a polymer or resin 4 thatcoats or impregnates an internal continuous single core or multistrandcore 6.

The fiber reinforced composite filament 2 is fed through a nozzlet 10heated (e.g., by a band heater or coil heater) to a controlledpush-pultrusion temperature selected for the matrix material to maintaina predetermined viscosity, and/or a predetermined amount force ofadhesion of bonded ranks, and/or a surface finish. The push-pultrusionmay be greater than the melting temperature of the polymer 4, less thana decomposition temperature of the polymer 4 and less than either themelting or decomposition temperature of the core 6.

After being heated in the nozzlet 10 and having the matrix material orpolymer 4 substantially melted, the continuous core reinforced filament2 is applied onto a build platen 16 to build successive layers 14 toform a three dimensional structure. One or both of (i) the position andorientation of the build platen 16 or (ii) the position and orientationof the nozzlet 10 are controlled by a controller 20 to deposit thecontinuous core reinforced filament 2 in the desired location anddirection. Position and orientation control mechanisms include gantrysystems, robotic arms, and/or H frames, any of these equipped withposition and/or displacement sensors to the controller 10 to monitor therelative position or velocity of nozzlet 10 relative to the build platen16 and/or the layers 14 of the part being constructed. The controller 20may use sensed X, Y, and/or Z positions and/or displacement or velocityvectors to control subsequent movements of the nozzlet 10 or platen 16.For example, the three dimensional printer 1000 may include arangefinder 15 to measure distance to the platen 16, a displacementtransducers in any of three translation and/or three rotation axes,distance integrators, and/or accelerometers detecting a position ormovement of the nozzlet 10 to the build platen 16. As depicted in FIG.1A, a (e.g., laser) range sensor 15 may scan the section ahead of thenozzlet 10 in order to correct the Z height of the nozzlet 10, or thefill volume required, to match a desired deposition profile. Thismeasurement may also be used to fill in voids detected in the part. Therange finder 15 may measure the part after the filament is applied toconfirm the depth and position of the deposited bonded ranks.

The three dimensional printer 1000 may include a cutter 8 controlled bythe controller 20 that cuts the continuous core reinforced filament(e.g., without the formation of tails) during the deposition process inorder to (i) form separate features and components on the structure aswell as (ii) control the directionality or anisotropy of the depositedmaterial and/or bonded ranks in multiple sections and layers. Asdepicted the cutter 8 is a cutting blade associated with a backing plate12 located at the nozzlet outlet. Other cutters include laser,high-pressure air or fluid, or shears.

FIG. 1A also depicts at least one secondary print head 18 optionallyemployed with the three dimensional printer 1000 to print, e.g.,protective coatings on the part including 100% resin FFF extrusion, a UVresistant or a scratch resistant coating.

FIG. 1B depicts an embodiment of a three dimensional printer 3001 inapplying a fiber reinforced composite filament 2 to build a structure.Like numbered features are similar to those described with respect toFIG. 1A.

As depicted in FIG. 1B, upstream of a driven roller 42 and an idleroller 40, a spool (not shown) supplies under mild tension an unmeltedvoid free fiber reinforced composite filament. The filament including atleast one axial fiber strand extending within a matrix material of thefilament, having no substantial air gaps within the matrix material. Inthis example, the fiber reinforced composite filament 2 is apush-pulpreg including a nylon matrix 4A that impregnates hundreds orthousands of continuous carbon fiber strands 6A.

A “zone” as discussed herein is a segment of the entire trajectory ofthe filament from the spool (not shown) to the part. The driven roller42 and an idle roller 40 feed or push the unmelted filament at a feedrate (which is optionally variably controllable by the controller 20,not shown, and optionally is less than the printing rate, with anydifferential between these rates absorbed along the filament by a slipclutch or one-way bearing), along a clearance fit zone 3010, 3020 thatprevents buckling of filament. Within a non-contact cavity ornon-contact zone 714, the matrix material of the composite filament maybe heated. The fibers 6A within may be under axial compression at thethreading stage or beginning of the printing process, as the feeding orpushing force of the rollers 42, 40 transmits through the unmeltedmatrix to the fibers along the clearance fit zone 3010, 3020.

“Threading” is a method of pushing a pushpreg or push-pulpreg through anoutlet wherein the stiffness of the pushpreg or push-pulpreg issufficiently greater than the sticking/drag force (to prevent bucklingor flaring/jamming of the pushpreg or push-pulpreg) over the time scaleof the stitching operation. Initially, in a threading stage, the meltedmatrix material 6A and the axial fiber strands 4A of the filament 2 arepressed into the part with axial compression, and as the build platenand print head are translated with respect to one another, the end ofthe filament contacts the ironing lip 726 and is subsequentlycontinually ironed in a transverse pressure zone 3040 to form bondedranks in the part 14. Transverse pressure means pressure to the side ofthe filament, and is also discussed herein as “ironing”. As shown by thearrow, this transverse pressure zone 3040 (along with attached parts ofthe print head) may be translated adjacent to the part 14 at a printingrate (or the printing rate may be a result of translation of both oreither one of the platen 16 and print head).

The matrix material is, in this example, with respect to tensile andcompressive elastic modulus, a thermoplastic resin having an unmeltedelastic modulus of approximately 0.1 through 5 GPa and a melted elasticmodulus of less than 0.1 GPa, and the fiber strands are of a strandedmaterial having an elastic modulus of approximately 5-1000 GPa. In thismanner, the strands of fiber are sufficiently resistant to deformationto enable the entire filament to be “pushed” through limited friction insmall clearance channels, and even through free space when the matrix ismelted. With respect to tensile ultimate strength, the matrix materialis preferably a thermoplastic resin having an unmelted ultimate tensilestrength of approximately 10 through 100 MPa and a melted ultimatetensile strength of less than 10 MPa, and the at least one axial strandincludes a stranded material having an ultimate tensile strength ofapproximately 200-100000 MPa. In this manner, the internal strands offiber are sufficiently resistant to stretching or snapping to enable theentire filament to be maintained in neutral to positive (i.e., from zerotension and higher amounts of tension) tension over significantdistances extending through free space from the bonded ranks, in somecases before the matrix fully solidifies. Most filaments will have across sectional area greater than 1×10⁻⁵ (1×10E-5) inches and less than2×10⁻³ 2×10E-3 inches. In the case of multi-strand fibers, the filamentmay include, in any cross-section area, between 100 and 6000 overlappingaxial strands or parallel continuous axial strands (particularly in thecase of carbon fiber strands).

Either or both of the printing head or nozzlet 708 or the build platform16 may be translated, e.g., the feed rate and/or the printing rate arecontrolled to maintain compression in the filament in the threadingstage, and to maintain neutral to positive tension in the printingoperation. The matrix material 4A of the filament 2 may be heated andmelted in the non-contact zone 3030 (in particular, so that there isless opportunity to stick to the walls of the nozzlet 708), but ismelted or liquefied at the ironing lip or tip 726. The larger ordiverging diameter of the non-contact zone optionally prevents thefilament from touching a heated wall 714 of the cavity defining thenon-contact zone . The feed and printing rates may be monitored orcontrolled to maintain compression, neutral tension, or positive tensionwithin the unsupported zone as well as primarily via axial compressiveor tensile force within fiber strand(s) extending along the filament.

As shown in FIG. 1B, the transverse pressure zone 3040 includes anironing lip 726 that reshapes the filament 2. This ironing lip 726 maybe a member that compacts or presses the filament 2 into the part tobecome bonded ranks. The ironing lip 726 may also receive heat conductedfrom the heated walls 714 or other heat source, in order to melt orliquefy the matrix material 4A of the filament 2 in the transversepressure zone 3040. Optionally, the ironing lip 726 in the transversepressure zone 3040 flattens the melted filament 2 on the top side,applying an ironing force to the melted matrix material and the axialfiber strands as the filament 2 is deposited in bonded ranks. This maybe facilitated by ensuring that the height of the bottom of the ironinglip 726 to the top of the layer below is less than the diameter of thefilament. Another reshaping force is applied spaced opposite of theironing lip 726 to the melted matrix material and the axial fiberstrands as a normal reaction force from the part itself. This flattensthe bonded ranks on at least two sides as the melted matrix material 4Aand the axial fiber strands 6A are pressed into the part 14 in thetransverse pressure zone 3040 to form laterally and vertically bondedranks (i.e., the ironing also forces the bonded ranks into adjacentranks).

Accordingly, the ironing lip 726 and the normal reaction force from thepart itself oppose one another and sandwich or press the meltedcomposite filament therebetween to form the bonded ranks in the part 14.The pressure and heat applied by ironing improves diffusion and fiberpenetration into neighboring ranks.

As shown in FIG. 1B, in this example, unmelted fiber reinforced filamentis cut at or adjacent the clearance fit zone 3010, 3020. It may be cut,as shown in FIG. 1A, in a gap 62 between a guide tube 72 (having aclearance fit) and the nozzlet 708, or may be cut within the nozzlet708, e.g., upstream of the non-contact zone 3030. Alternatively or inaddition, the core reinforced filament may be cut by a cutter 8positioned at or adjacent either one of the clearance fit zone 3010,3020 or the ironing lip 725. The clearance fit zone 3010, 3020 includesan optionally interrupted channel forming a clearance fit about thefiber reinforced composite filament 2, and this is preferably one of arunning fit or a clearance location fit, in any even sufficientclearance to permit the filament to be pushed along, even in axialcompression, without sticking and without buckling.

The pushing/feeding along the axial direction, and ironing within thetransverse pressure zone 3040 are not necessarily the only forcesforming the bonded rows. Alternatively, or in addition, the transversepressure zone 3040 and/or ironing lip 726 are translated respective tothe part 14 at a printing rate that maintains neutral to positivetension in the fiber reinforced composite filament 2 between the ironinglip 726 and the bonded ranks of the part 14, this tension being lessthan that necessary to separate a bonded rank from the part 14.

For example, after the matrix material 6A is melted by the ironing lipor tip 726, the feed and/or printing rate can be controlled by thecontroller 20 to maintain neutral to positive tension in the compositefilament 2 between the ironing lip 726 and the part 14 primarily viatensile force within the fiber strands 4A extending along the filament2. This is especially the case at the end of bonded ranks and in makinga turn to begin a new adjacent rank in the opposite direction, aspressure from the ironing lip into the part 14 may be released. This canalso be used to form bridges through open space, e.g. by drawing thefiber reinforced composite filament 2 in the transverse pressure zone3040 from a connection to a first portion of the part 14; thentranslating the transverse pressure zone 3040 through free space; thenironing to reconnect the fiber reinforced composite filament 2 to asecond portion of the part 14.

Unlike a true extrusion process, the cross sectional area of thefilament 2 is substantially maintained the entire time, and none of thestrands, the matrix, nor the filament 2 lengthens nor shortensappreciably. The feed rate of the spooled push-pulpreg and the formationrate (the printing rate) of the bonded ranks are substantially the same(although for portions of the conveyance or feeding, slip clutches orone-way bearings may permit slack, build-up or differential). At times,the feed rate and the compression rate may be temporarily anddifferentially controlled to balance sufficient neutral to positiveaxial tension downstream of the ironing lip 726, or a slip clutch may beused to allow one of feed rate or printing rate to slip. However, asubstantially constant cross sectional area of the fiber reinforcedcomposite filament is maintained in the clearance fit zone, theunsupported zone, the transverse pressure zone, and also as a bondedrank is attached to the workpiece or part 14.

FIG. 2 presents a schematic flow diagram of a three dimensional printingprocess using the system and controller depicted in FIG. 1A or 1B. InFIG. 2, optional steps of the invention that individually or in anycombination may modify some versions of the invention disclosed in FIG.2 are denoted with dotted lines and an “A” suffix, although none of thesteps shown are individually critical or in the particular order shown,except as inherently necessary. Initially a continuous core ormultistrand fiber reinforced filament 2 is supplied (e.g., from a spool,as a push-pulpreg) at step S103. As shown in step S103A, supplying incartridge form can be important, as it permits complete independencebetween processes of manufacturing the push-pulpreg and printing. Thatis, either manufacturing of push-pulpreg or printing could be a limitingspeed factor, and by using prepared cartridges or rolls ofinterchangeable filament, each is made independent. In step S105, thefilament 2 is drawn from the supply or spool (e.g., by rollers) and fedin an unmelted, relatively stiff state through a clearance fit, or asuccession of clearance fits, that may prevent buckling of the filamentas it is pushed and fed. Optionally, as shown in step S105A, during thethreading or stitching process, the filament is fed in a manner thatkeeps axial compression in the filament 2 downstream of the feed (notingthat this may change into axial neutral or positive tension in optionalstep S113A after the lateral pressing step S111) into the heated nozzlet708.

In step S107, the filament (and thereby the matrix material) is heatedto a desired temperature that is greater than a melting temperature ofthe resin and is less than a melting temperature of the continuous coreor strands at step S107. This completion of this step may be out oforder with respect to that shown in FIG. 2, i.e., the heating of theironing tip 726 or other heating zone may be initiated at step S107, butthe actual melting may take place only in step S11A. Moreover theheating zone may be the final zones along the path, i.e., the ironingtip or non-contact zone, as shown in optional step S107A. This stepmelts the matrix material throughout and permits the shape of thefilament to change, e.g., from a circular cross section or an oval crosssection to a square or rectangular cross section as it is packed/pressedinto the part, while nonetheless keeping a substantially similar oridentical cross sectional area. As noted in optional step S107A, thisheating may take place in or at an ironing tip 726 at the tip of thenozzlet. Further, within a non-contact the zone 714 or 3030, the wallsof the nozzlet 708 are sufficiently distant from the filament 2 suchthat even heating into a plastic, glass transition or tacky form willnot adhere the filament to the walls. At step S108, the controller 20 ofthe three dimensional printer 1000, 3001 controls, (optionally in stepS108A using the sensors described herein), position, speed, oracceleration of the nozzlet 708 relative to the build platen 16 or part,and may also monitor distances therebetween and temperature propertiesat each zone or within each zone.

In step S110, while controlling the position and movement of the heatednozzlet 708, the controller 20 controls the feed rate, print rate,cutter 8 and/or temperatures to maintain an axial compression in theclose fitting zone 3010 or 3020 (upstream and downstream of a cutter 8)and the heating and/or non-contact zone 714, 3030 in the threadingphase, or, in the printing phase; and/or controls pressing, compressing,or flattening pressure or force within zone 3040; and/or in the printingphase controls axial neutral to positive tension within the filamentbetween the bonded ranks within the part 14 and the lateral ortransverse pressure zone 3040 and/or ironing lip 208, 508, and/or 726.

In step S111, under the control of the controller 120, the filament(matrix and fibers) 2 is pressed into the part 14. Optionally, as shownin step S111A, this is performed with an ironing lip or tip 208, 508,and/or 726, which may be smooth but also may be more like a doctor blade(for abrasion resistant fibers such as aramid). Simultaneously, thepressing zone 3040 and/or built platen or platform 16 are translated(optionally in 3 axes, and further optionally rotated in 3 rotationalaxes) with respect to one another at step S113. Optionally as shown byoptional step S113A, in this step S113, neutral or positive tension ismaintained and/or increased in the filament between the tip 208, 508,and/or 726 and the part 14.

In step S115, the ironing (pressing and heating) and relativetranslating (or relative printing motion for multi-axis implementations)adheres the bottom and sides of melted matrix within the filament 2 toform bonded ranks in the part 14. As discussed herein and as shown instep S115A, these ranks may optionally be tight boustrophedon ranks, maybe circular, oval, or oblate loops (e.g., racetrack shapes for longparts), may proceed with small turns in a “Zamboni” pattern, and in anyof these patterns or other patterns may be successively laid up suchthat one layer is parallel with or overlapping the layer below, or istransverse to (perpendicular or angled) to the layer below.

In step S117, after reaching the desired termination point, thecontinuous core reinforced filament may be cut. As discussed in stepsS117 and S117A, “cut” includes cutting at a position within thecompression zone 3010, 3020, in particular upstream of the nozzlet 8,and in particular of the filament in an unmelted, glass state of thematrix material. “Cut” may also include cutting at a position indownstream or adjacent of the nozzlet 708. In addition, “cut” mayinclude, for embodiments in which the continuous strands are formed indiscrete, separated segments within the filament, pulling the nozzlet708 and build platen 16 away from one another to separate the matrixmaterial at a location where one segment of continuous fiber is adjacentthe next. The controller 20 may then determine if the three dimensionalpart is completed. If the printing process is not completed thecontroller may return to step S108 during which it senses the currentposition and movement of the nozzlet prior to depositing the next pieceof continuous core reinforced filament. If the part is completed, thefinal part may be removed from the build platen. Alternatively, anoptional coating may be deposited on the part using a secondary printhead at S121 to provide a protective coating and/or apply a figure orimage to the final part.

FIGS. 3A-3D are schematic representations of a different possiblefilaments useful with the invention, although these are not necessarilyto scale. FIGS. 3A and 3B depict cross-sections having a solidcontinuous core 6 a (e.g., a fiberglass fiber) and surroundingthermoplastic polymer 4 or resin, respectively greater than 70% resin bycross-sectional area and less than 30% resin (each by cross-sectionalarea). FIGS. 3C and 3D depict cross-sections having multi-strand fiberssurrounded by and wicked/wetted by thermoplastic resin, respectivelygreater than 60% resin and all fibers being ¼ diameter or more from theperimeter; and less than 30% resin with fibers distributed throughoutthe filament and protruding from the perimeter. FIG. 4 depicts across-section similar to FIG. 3D but including one or more separatesecondary functional strands 6 c and 6 d (with electrical, optical,thermal or fluidic conducting properties to conduct power, signals,heat, and/or fluids as well as for structural health monitoring andother desired functionalities). For carbon fiber, resin amounts forprinting in push-pulpreg manner are from 30-90% (i.e., 10-70% fiber bycross sectional area).

According to one version of the present invention, the polymer materialis pre-impregnated as a push-pulpreg such that the molten polymer orresin wicks into the reinforcing fibers during the initial production ofthe material, optionally into the entire cross-section of amultifilament. Optionally per this aspect of the invention, strands offiber may be pre-treated with a coating(s) or agents, such as aplasticizer, energy application by radiation, temperature, pressure, orultrasonic application to aid the polymer or resin wicking into thecross section of the multifilament core without voids. The heatingtemperature of the printing process in zone 3030 may be at a lowertemperature and/or higher viscosity of melted material than thetemperature or energy necessary to accomplish wetting, wicking, tacking,or interstitial penetration at lower viscosity to fill voids. Preparingthe push-pulpreg as a void-free prepreg permits filament width and otherproperties (e.g., stiffness, smoothness) to be predetermined, reducingthe need for complicated measurement and variable control for differentfilaments (of the same type, or of different types).

According to one version of the present invention, a vacuum is providedwithin the heated section 714 of nozzlet 708 to remove air (includingvoids) while the matrix material is melted. This construction may beused even with filaments which may have air voids within (e.g., “greenmaterial”) including a solid or multifilament core while under vacuum.In the alternative to or in addition to the vacuum removal of voids thepresent invention, the filament may be forced through a circuitous path,which may be provided by offset rollers or other configurations, tomechanically work out entrapped air.

FIG. 5 depicts a hypothetical and theoretical problem, unknown in theprior art, in which the present inventor contemplated whether a knownconvergent nozzle could be used with towpreg or other embedded fibercomposite filament. The matrix material as a polymer has a largercoefficient of thermal expansion (even in the case of a polymer fibersuch as aramid). As the matrix material is heated it is believed itwould accelerates relative to the fiber due to the larger expansion ofthe matrix material within the confined space of the converging nozzle.The matrix material flow rate Vmatrix is less than the fiber materialflow rate Vfiber near the nozzle inlet, yet the matrix material flowrate at the outlet Vmatrix' is equal to the fiber material flow rateVfiber. As illustrated in the FIG. 5, the mismatched velocities of thematrix material and fiber within the converging nozzle may result in thefiber collecting within the nozzle during the deposition process,leading to at least clogging and poor uniformity in deposition. Whilethe present inventor does not believe the converging nozzle is theoptimal solution, nonetheless it is within the scope of the presentembodiments.

A family of straight and diverging nozzlets which maintain a matchedvelocity of the strand(s) of fiber material 6 b and the polymer matrix 4throughout the entire nozzlet (at least so that the matrix does notbuild up within) are shown in FIGS. 6A through 6C. FIG. 6A depicts adivergent nozzlet 200 with an increasing nozzlet throat diameter thatmatches the thermal expansion of the matrix material, the nozzlet 200including an inlet 202 with a diameter D1, a section with an increasingdiameter 204, and an outlet 206 with a diameter D2 that is greater thanthe diameter D1. Alternatively, where both the matrix material and thefiber strand(s) have relatively low coefficients of thermal expansion(such as carbon fiber and Liquid Crystal Polymer), the nozzlet 200 mayinclude an inlet 202 and outlet 206 that have substantially the samediameter D3, see FIG. 6B. A nozzlet 200 or 708 may also include arounded outlet 208 or 726, as shown in FIG. 6C. For example, the roundedoutlet 208 may be embodied by an outwardly extending lip, a chamfer, afilet, an arc, or any other appropriate geometry providing a smoothtransition from the outlet, which may help to avoid fracture, applyingstresses to, and/or scraping, the filament as it is printed.

FIG. 7 illustrates a hypothetical and theoretical problem, unknown inthe prior art, in which a print head 300 is forming part 302, havingdeposited the last section of material layer 304. The print head 300touches the top of the extruded plastic, leaving no room for a cutter.If this print head were a push-pultrusion printer discussed herein butlacking the optional cutter 8, 8A discussed herein, the print head wouldprint a tag-end over-run 306 not modelled (i.e., to be removed later) inthe part in order to enable a subsequent cutting process to cut theembedded strand (and matrix) and terminate a printing process. In somecases, this may be desired (e.g., for conductive fibers). In othercases, this would create undesired tag-end overruns, e.g., as shown inFIG. 7, each of many hard mounting bosses 308 would all have a tag-endover-run 306 at each layer within the boss.

FIG. 8 depicts two embodiments of a cutter for use with a threedimensional printer. Like elements described with reference to, e.g.,FIG. 1A or 1B are substantially similar. As depicted, a filament 2 or 2a, is supplied from a spool 38 and drawn and fed by driving roller 40and idle wheel 42, which apply a force directed in a downstreamdirection to the filament 2 a. Unheated, or at ambient or roomtemperature, or in any case below glass transition temperature in thiszone (3010 or 3020), the matrix of the filament 2 a is in a solid or“glass” state when this force is applied. The applied downstream force,as discussed herein, is transmitted via the glass state matrix 4A to thefiber strands 6A, which pushes the entire filament from a heated nozzlet10 to build up a three dimensional part, despite that the matrix is thenmelted. The position of a cutter 8, 8 a, 8 b may reduce or eliminate thepresence of tag-end over-runs in the final part, or permit them to beflexibly created if advantageous.

Positioning the cutter 8 a (e.g., blade) at the outlet of the nozzlet 10allows actuation of the cutter 8 a to completely cut the deposited stripor bonded rank by severing the internal fiber strands, and/or mayprevent further advance and/or dripping by physically blocking thenozzlet outlet. A cutter 8 a or 8 b enables the deposition of filament(fiber reinforced or unreinforced) with precisely controlled lengths ascontrolled by the controller 20. In the alternative, positioning acutter 8 b upstream from the nozzlet 10, between the nozzlet 10 outletand the feeding mechanism 40, permits a smaller gap between the nozzlet10 outlet and the part. In the alternative or addition, the cutter 8 bmay cut the filament while the matrix temperature is below a melting,softening, or glass transition temperature, reducing the propensity ofthe resin to stick to the blade which may reduce machine jamming; and/orenable more precise metering of the deposited material.

If a relatively close (but in no circumstances binding) fit ismaintained between the filament 2 and a guiding tube shown in FIG. 10(which may be a clearance fit 3010 or larger guide), a downstreamportion 2 b of the cut strand is pushed by the abutting upstream portion2 a is driven by the drive roller 40. The previously bonded ranks(cooled) are adhered and under tension “drag” filament 2 b from of thenozzlet 10 as the nozzlet 10 and build platen 16 are moved relative toone another. A combination of upstream forces from the feeding mechanismand downstream forces transferred via the unmelted or glass portion ofthe filament and the strands of the filament are used to deposit thebonded ranks.

As noted, a cutter 8, 8 a, 8 b is optional, but may also preventbuckling of the material to help ensure a uniform deposition and preventmachine jams. Further, small diameter (e.g., less than 30 thou)continuous filament is more susceptible to buckling. In this case, aclose-fitting guide tube 10, or close-fitting guide within 64, 712 (inzones 3010, 3020) adjacent the feeding mechanism 42, 40 and/or near tothe nozzlet 708 outlet, may help prevent buckling of the material.Therefore, in one embodiment, the feeding mechanism 42, 40 may belocated within less than about 3-8 diameters from a guide tube or inletto the nozzle. In one specific embodiment, the guide tube is a roundhypodermic tube. However, if the filament is shaped other thancircularly (e.g., oval, square, or tape), the guide tube is sized andshaped to match. Optionally, the filament 2 may include a smooth outercoating and/or surface where the fibers do not protrude through thefilament 2 perimeter (reducing friction or resistance within the guidetube).

In some embodiments, the three-dimensional printing system does notinclude a guide tube. Instead, the feeding mechanism may be locatedclose enough to an inlet of the nozzle, such as the receiving tube 64,such that a length of the continuous core filament 2 from the feedingmechanism to an inlet of the nozzlet is sufficiently small to avoidbuckling. In such an embodiment, it may be desirable to limit a forceapplied by the feeding mechanism to a threshold below an expectedbuckling force or pressure of the continuous core filament, or othermaterial fed into the nozzle.

In some embodiments, the maximum tension or dragging force applied tothe deposited reinforcing fibers is limited to prevent the printed partfrom being pulled up from a corresponding build plane or to provide adesired amount of neutral to positive tensioning of the continuous core.For example, a one-way locking bearing may be used to limit the draggingforce (e.g., with the speed of the feeding rollers set to be less thanthe speed of printing, but with the one-way bearing permitting thefilament to be pulled through the rollers faster than they are driven).In such an embodiment, the drive motor 42 may rotate a drive wheelthough a one-way locking bearing such that rotating the motor drives thewheel and advances material. If the material dragging exceeds the drivenspeed of the drive wheel, the one-way bearing may slip, allowingadditional material to be pulled through the feeding mechanism andnozzle, effectively increasing the feed rate to match the printing rateor head traveling speed while also limiting the driving force such thatit is less than or equal to a preselected limit. The dragging (neutralto positive tension) force may also be limited using a clutch withcommensurate built-in slip. Alternatively, in another embodiment, thenormal force and friction coefficients of the drive and idler wheels maybe selected to permit the continuous material to be pulled through thefeeding mechanism above a certain dragging force. Alternatively or inaddition, an AC induction motor, or a DC motor switched to the “off”position (e.g. a small resistance applied to the motor terminals oropening motor terminals) may be used to permit the filament to be pulledfrom the printer against motor resistance. In such an embodiment, themotors may be allowed to freewheel when a dragging force above a desiredforce threshold is applied to allow the filament to be pulled out of theprinter. In view of the above, a feeding mechanism is configured in someform or fashion such that a filament may be pulled out of the printernozzlet when a dragging force applied to the filament is greater than adesired force threshold. Additionally, in some embodiments, a feedingmechanism may incorporate a sensor and controller loop to providefeedback control of either a deposition speed, printer head speed,and/or other appropriate control parameters based on the tensioning ofthe filament.

According to the versions of the invention discussed herein, theprinting process may be similar in all phases, or create a differentbalance of forces within the printer, filament, and part in differentprinting phases (e.g., threading phase versus printing phase, and/orstraight phases versus curved phases). For example, in one version ofthe invention, the printer may apply bonded ranks primarily via lateralpressing and axial tension in the main, continuous printing phase, andprimarily via lateral pressing and axial compression in the threadingphase where the end of the filament is first abutted to the platen orpart and then translated under the ironing tip to be melted.

According to the versions of the invention discussed herein, theprinting system may, under axial neutral to positive tension, drag afilament 2 out of a printer nozzlet 708 along straight printed sections(and this tension extends past the nozzlet 708 to the feeding mechanism42, 40 controlled at a feed rate, but which may have a slipping orclutch mechanism). During such operation, a printer head may bedisplaced or translated at a desired rate by the controller 20, and thedeposited material and/or bonded ranks which are adhered to a previouslayer or printing surface will apply a dragging force to the filamentwithin the printing nozzle. The filament is pulled out of the printingsystem and deposited onto the part 14. In contrast, in addition, or inthe alternative, according to the versions of the invention discussedherein, when printing along curves and/or corners, the feeding mechanism42, 40 feed rate, and printing rate of the printing system may becontrolled by the controller 20 to pushes the deposited filament onto apart or build surface 16. However, versions of the invention andembodiments in which a filament is pushed out of the printing systemduring a straight operation and/or where a filament is dragged out of aprinter head when printing a curve and/or corner are also contemplated,as well as versions where the filament is substantially always draggedor substantially always pushed.

The deposition of tensioned internal strand reinforced filamentsincluding a non-molten strand enables the deposited material to bepushed by the print head and adhered to the printed part at the (distal)end. The print head can suspend the filament across an open gap undertension, without the material sagging, enabling the construction ofhollow-core components (with or without the use of soluble supportmaterial).

FIG. 8 depicts free-space printing enabled by the continuous corereinforced filament. With the continuous core reinforced filament 2 battached to the part at point 44, and held by the print head at point46, it is possible to bridge the gap 48. Absent the tensioned internalfiber strands, the molten matrix material would sag and fall into thegap 48. In one example, the closed section box shown in FIG. 9 is formedby a section 50 which is bridges gap 48 and is affixed to opposingsections 52 and 54. Such free-space printing could also be used toproduce cantilever beams that cannot be printed with typical unsupportedmaterials. In such a case, optionally, a cooling mechanism such as a jetof cooling air may further prevent sagging by solidifying the polymermaterial surrounding the core, either continuously cooled over theentire or most of the build area during gap spanning, or cooled at thepoint of material advance during gap spanning. Selectively coolingmaterial only while it is over a gap may lead to better adhesion in theremaining part since maintaining an elevated enhances diffusion bondingbetween adjacent layers.

In the above noted embodiments, a cutting blade is located upstream ofthe nozzlet to selectively sever a continuous core when required by aprinter. While that method is effective, there is a chance that atowpreg will not “jump the gap” correctly between the cutter and thenozzle. Consequently, in at least some embodiments, it is desirable toincrease the reliability of rethreading the core material after thecutting step. A cutter may be designed to reduce or eliminate theunsupported gap after the cutting operation, e.g., a tube-shaped shearcutter in which two abutting and coaxial tubes guiding the filament aretemporarily displaced with respect to one another to shear the filament.

FIG. 10, similar to FIGS. 1A and 1B, depicts a printer mechanism. Likereference numerals and parts by appearance describe similar features.The filament 2 which is drawn into the feed rollers 40, 42 undertension, and to facilitate guiding and maintaining alignment of thefilament 2 with the rollers 40, 42, the filament 2 passes through aguide tube 74 upstream of the rollers 40, 42. After passing through therollers, 40, 42 the continuous core filament 2 is in axial compression(at least sufficient to overcome friction through any guiding tubes orelements). Depending on a length of the material under compression aswell as a magnitude of the applied force, the continuous core filament 2may tend to buckle. Accordingly, the continuous core filament 2 passesthrough a close-fitting guide tube 72 (e.g., clearance fit) positioneddownstream of the rollers 40, 42 and upstream of the nozzlet 68. Theguide tube 72 both guides the filament 2 and prevents buckling of thecontinuous core filament 2. A gap 62 is present between the printer head70 and the cutter 8.

When the filament 2 is cut, the filament 2 is “rethreaded” passing fromone side of the gap 62 to the receiving guide tube 64. The receivingtube 64 itself is optionally below the glass transition temperature ofthe material. Optionally, a thermal spacer 66 between the receiving tube64 and heated part of the nozzlet 68 reduces the heat transfer to thereceiving tube 64 from the hot nozzlet 68. FIG. 11 is a photograph of asystem including the above-noted components, showing the roller 40, 42,close fitting tube 72, and filament 2 (which are each of very smalldiameter, between 10 and 50 thou).

In FIG. 10, difficulty in rethreading (i.e., through the entire system,versus during the threading or stitching process through the terminalend of the printhead which initiates printing) may be encounteredbecause the filament is more flexible and prone to bending or bucklingwhen the end is unsupported, than after it has been threaded and bothends are fully supported and constrained in a first order bending mode.After the filament has been threaded, the downstream portion guides allthe subsequent filament. Cutting a filament, especially with a dull orthick blade, may also deform the end of the filament, tending toincrease misalignment of the filament 2 and the receiving tube 64.

To improve the reliability of threading the filament past the cutter 8,8 a, or 8 b, when not in use, the cutter 8 is removed from the gap 62and the guide tube 72 is displaced (down) and/or telescoped towards thereceiving tube 64 during rethreading. The clearance (gap) between theguide tube 72 and receiving tube 64 may be reduced, or the tubes 64, 72may abut. Alternatively, pressurized fluid, such as air, may also bedirected axially down the guide tube 72, such that the axial fluid flowcenters the material to align the material with the receiving end 16(and may cool the guide tube 72 tube for high-speed printing and/orhigher printing temperatures, and/ reduce friction of the materialthrough the guide tube.

FIGS. 12A, 12B, and 13 depict embodiments of shear cutters, each ofwhich eliminates the gap 62 to increase reliability of threading. Theshear cutter may be optionally located within a print head, or upstreamof the print head; and relative movement of shearing blocks is moreimportant than which block moves. In FIG. 12A, the continuous filament400 is driven in compression by drive wheel 408, and received by aclose-fitting guide tube 420. The filament 2 is driven in compressionthrough an upper shear cutting block guide 406, lower shear cutting head402, and heated print head 404. The upper shear cutting block 406 andlower shear cutting head 402 are displaced relative to each other toapply a shearing force to the filament to cut it. FIG. 12B shows theupper shear cutting block 406 translated relative to shear cutting head402, shearing off the filament segment 422. If a simple cut is desired,the shear head 402 can return to the original position relative to theupper cutting block 406. After the shear cut and return, the end of thefilament 400 is entirely captive in the guiding tube. There is no gap tojump.

It may be desirable to provide printing capabilities with multiple typesof materials and/or operations. FIG. 12A illustrates one embodiment of asystem including optional indexing stations 414 and 416. In oneembodiment, station 416 is a cleaning station and includes an optionallymetal cleaning material 410 (e.g., brass, copper, stainless steel,aluminum), that can be fed through the print head 404 to clean thenozzlet, enabling the nozzlet to be heated, and purged with a materialhaving a higher melting temperature than the filament 2. One process maybe: the print head 404 is moved to a print cleaning station at a theback corner or other appropriate location; is then heated up and indexedto station 416; then the cleaning material 410 is then fed through thenozzlet to clear any obstructions. The upper sheer cutting block 406 andthe lower shear cutting head 402 can then sever the sacrificial cleaningpieces to prevent introducing contaminants back to the nozzle.Alternatively the cleaning agent may be cyclically pushed down, andpulled back up through the nozzle. In another embodiment, the cleaningstation 416 is used to push cleaning agents such as high-pressureliquids, gasses, solvents or the like, through the nozzle.

In some embodiments, the three-dimensional printing system may include astation 414 corresponding to a second filament 412, which may be anelectrically conductive material such as copper, an optically conductivematerial such as fiber optics, a second core reinforced filament,plastics, ceramics, metals, fluid treating agents, solder, solder paste,or epoxies, etc. The print nozzle or nozzlet 404 is indexed from one ofthe other stations to the station 414 to deposit the second material412, and back when completed.

FIG. 13 shows a shear cutting block 402 including multiple nozzles 404and 424 formed in the shear cutting block. In one embodiment, thenozzlet 404 has a larger print orifice than the nozzlet 424, enablinglarger diameter push-pulpreg and/or pure polymer materials to bedeposited at a more rapid volume. In another embodiment, the secondnozzlet 424 is substantially the same as nozzlet 404. Consequently, thesecond nozzlet 424 may be used as a replacement nozzlet that can beautomatically switched into use if nozzlet 404 becomes clogged. Havingan additional nozzlet would decrease the down time of the machine,especially in unattended printing (e.g. overnight). Similar to theabove, the first and second nozzles 404 and 424 may be indexed betweendifferent stations.

FIGS. 14A-14C depict a family of nozzlets having different outlets. FIG.14A depicts a nozzlet 500 including an inlet 502 and an outlet 504 whichincludes a sharp exit corner suitable for some filaments 2 such asaramid, but which may lead to damage to fibers which are not resistantto abrasion, such as fiberglass, carbon, plating on metal cores,treatments to fiber optic cables. FIG. 14B depicts a smooth transition,multiple chamfered (e.g., twice chamfered, or 45 degree) nozzlet outlet506, which reduces shear cutting of fibers, and FIG. 14C depictssmoothly rounded nozzlet exit or ironing tip 508 which reduces shearingand cutting of non-molten strands.

It may, in the alternative, be desirable to sever the filament 2, e.g.,by pushing a sharp edged nozzlet down in the vertical Z direction, asshown by arrow 510. As depicted in FIG. 14C, the corner of a nozzlet 508may be sharpened and oriented in the Z direction to sever the continuouswhen forced against the filament 2 (optionally under tension, optionallyprovided by any or all of driving the feeding mechanism and/or movingthe print head, or moving the build table). As depicted in in FIGS.15A-15D, a portion of a nozzlet is optionally be sharpened and directedtowards an interior of the nozzlet outlet to aid in cutting materialoutput through the nozzlet. As shown, smoothly chamfered nozzlet 600contains a filament 2, exiting from a chamfer nozzlet 600, and a ring602 located at a distal outlet of the nozzlet. A first portion of thering 602 is non-cutting and shaped and arranged to avoid interferingwith the filament 2, and a second portion of the ring 602 includes acutting portion or blade 602 a (optionally steel, carbide, or ceramic)sharpened and oriented inwards towards the filament 2 path containedwithin the nozzlet 600 as seen in FIGS. 15B-15D, and occupying less than1/10 of the nozzlet outlet area. The cutting portion 602 a may be anyof: permanently attached; selectively retracted during printing anddeployed to cut; recessed into a perimeter of the nozzlet outlet;forming a part of the perimeter of the nozzlet exit as depicted in FIG.15B; formed integrally with the nozzlet outlet; and/or attached to thenozzlet outlet.

In operation as shown in FIGS. 15A-15D, the nozzlet 600 is translated ina direction D relative to a part being constructed on a surface whilethe filament 2 is stationary and/or held in place, resulting in thetensioning of the core material 6. As increasing tension is applied tothe continuous core filament 2, the core 6 is cut through by the cuttingportion 602 a. Alternatively, the surface and/or part is translatedrelative to the nozzlet or the filament tensioned using the feedingmechanism to perform the severing action. FIG. 16 presents anotherembodiment of a nozzlet tip-based cutter m the depicted embodiment, acutting ring 604 having a sharp and edge oriented towards the alreadydeposited filament 2, which is actuated relative to the nozzlet 600 andpart to expose the sharp edge to bring the filament in contact with thecutting element 604, and sever the core material 6.

For brittle materials, such as fiber optic cables, the cutting portion602 a or 604 may form a small score, and additional relative translationof the nozzlet and the part may complete the cut. For other materials,such as composite fibers, the rounded geometry of the nozzlet results inthe core 6 being directed towards the cutting portion 602 a or 604 undertension, with resulting consolidation (e.g. compaction) toward thecutting portion enables cutting of a large fiber with a relativelysmaller section blade. For metal fibers or ductile materials, thecutting portion 602 a or 604 may create enough of a weak point in thematerial that sufficient tensioning of the core breaks the core strandat the nozzlet exit.

The cutting portion 602 a or 604 may be a high temperature heatingelement referred to as a hot knife, which may directly or indirectlyheat the fiber to a melting temperature, carbonization temperature, or atemperature where the tensile strength of the core is low enough that itmay be broken with sufficient tensioning. The heating element may be ahigh-bandwidth heater that heats quickly and cools down quickly withoutharming the printed part; or an inductive heating element that isolatesheating to the fiber.

According to versions of the present invention discussed herein, axialcompression and/or laterally pressing the melted matrix filament 2 intobonded ranks may enhance final part properties. For example, FIG. 17Ashows a composite fiber reinforced filament 2 applied with a compactionforce, axial compression, or lateral pressure 62. The compactionpressure from axial compression and flattening from the ironing lip 508,726, 208 in zone 3040, compresses or reshapes the substantially circularcross-section filament 2 a, see FIG. 17B, into the preceding layer belowand into a second, substantially rectangular cross-section compactedshape, see FIG. 17C. The entire filament forms a bonded rank (i.e.,bonded to the layer below and previous ranks on the same layer) as it isshaped. The filament 2 b both spreads and interior strands intrude intoadjacent bonded ranks 2 c on the same layer and is compressed into theunderlying shaped filament or bonded rank of material 2 d. Thispressing, compaction, or diffusion of shaped filaments or bonded ranksreduces the distance between reinforcing fibers, and increases thestrength of the resultant part (and replaces conventional techniquesachieved in composite lay-up using post-processing with pressure platesor vacuum bagging). Accordingly, in some versions of the presentinvention discussed herein, the axial compression of the filament 2and/or especially the physical pressing by the printer head 70, nozzletor ironing lip 508, 726, 208 in zone 3040 may be used to apply acompression pressure directly to the deposited material or bonded ranksto force them to spread or compact or flatten into the ranks besideand/or below. Cross-sectional area is substantially or identicallymaintained. Alternatively or in addition under versions of the presentinvention, pressure may be applied through a trailing pressure platebehind the print head; a full width pressure plate spanning the entirepart that applies compaction pressure to an entire layer at a time;and/or heat, pressure, or vacuum may be applied during printing, aftereach layer, or to the part as a whole to reflow the resin in the layerand achieve the desired amount of compaction (forcing of walls togetherand reduction and elimination of voids) within the final part.

As noted above, and referring to FIG. 18A, nozzles 700 used in FusedFilament Fabrication (FFF) three dimensional printers typically employ aconstriction at the tip of the nozzle 700, leading to eventual cloggingand jamming of the print head (nozzle). The nozzles on most FFFthree-dimensional printers are considered wear items that are replacedat regular intervals.

In a divergent nozzlet according to some versions of the presentinvention, material expands as it transitions from a feed zone, to aheated melt zone, enabling any particulate matter that has entered thefeed zone to be ejected from the larger heated zone. A divergent nozzletis both easier to clean, permitting permit material to be removed in afeed forward manner.

As used in the following discussion, “fluidly connected” is used in thecontext of a continuous connection permitting flow, and does not suggestthat the filament 2 is or is not fluid at any particular stage unlessotherwise indicated. FIG. 18B shows a nozzlet 708 including a materialinlet 710, connected to a cold-feed zone 712, in turn fluidly connectedto a heated zone 714. The cross-sectional area (perpendicular to flowdirection) of the cavity or channel in the heated zone 714 and/or outlet716 is greater than the cross-sectional area (perpendicular to flowdirection) of the cavity or channel located in the cold-feed zone 712and/or the inlet 710. The cold-feed zone 712 may be constructed of amaterial that is less thermally conductive than that of the heated zone714, permitting the filament 2 to pass through the cold feed zone 712and into the heated zone 714 without softening.

In one particular embodiment, the divergent nozzlet 708 is formed byusing a low-friction feeding tube, such as polytetrafluoroethylene, fedinto a larger diameter heated zone located within a nozzlet such that aportion of the heated zone is uncovered downstream from the tube. Theheating zone may in addition or in the alternative be constructed from,or coated with, a low friction material such as polytetrafluoroethylene,and the transition from the cold feed zone 712 to the heated zone 714may be stepped, chamfered, curved, or smooth.

FIG. 18C depicts an instance where a divergent nozzlet 708 has beenobstructed by a plug 718 that has formed during use within the heatedzone 714 and then removed. The divergent nozzlet 708 can be cleanedusing a forward-feeding cleaning cycle, e.g., starting by applying andadhering a portion of plastic onto a print bed or cleaning area adjacentthe print bed, after which the adhered plastic is cooled (left to cool)below its melting temperature, whereupon the print bed and nozzlet aremoved relative to each other to extract the plug 718 from the nozzlet708 (optionally helped by a unmelted compressive force from filamentupstream in the feeding mechanism). While any appropriate material maybe used with a divergent nozzle, nylon and nylon relatives areparticularly advantageous because nylon's coefficient of thermalexpansion for nylon causes it to pull away from the nozzlet slightlyduring cooling and nylons exhibit a low coefficient of friction.Polytetrafluoroethylene walls within either or both of the cold feed andheated zone may help with plug removal. A cleaning cycle may also beperformed without the adhering step by extruding a section of plasticinto free air, then removed by hand or using an automated tool.

In the case of a straight nozzlet, particularly for small diameterfilaments on the order of about 0.001″ up to 0.2″, as shown in FIG. 19A,a nozzlet 720 may include an inlet 724 that is substantially the samesize as nozzlet outlet 722. A material such as a stranded reinforcedcomposite filament 2 passes through a cold feed zone 712 and into aheated zone 714 (e.g., either or both zones low friction and/orpolytetrafluoroethylene walled). The heated zone 714 is thermallyconductive, e.g., made from copper, stainless steel, brass, or the like.The filament 2 is attached to a build platen 16 or cleaning area, andthe process describe with respect to FIGS. 18B and 18C carried out.Small diameter filaments are suited to this because the low thermal masspermits them to heat up quickly and be extruded (in the case of FFF) atsubstantially the same size as they are fed into the print head. FIG.19B shows a hypothetical manner in which a conventional green towpregmay come apart in a straight nozzlet.

FIGS. 19C-19E illustrate a method of threading according to versions ofthe present invention using a rigid push-pulpreg stranded filament fedthrough a divergent nozzlet 708, such that clogging is reduced oreliminated. “Threading”, in this context, is the first step in printingof continuous deposition (straight sections and rows) of bonded ranks,and is only performed again after the filament 2 is cut, runs out, isseparated, or otherwise must be again started. FIG. 19C shows acontinuous core filament 2 located within a cold feed zone 712, whichmay begin 5 inches or more from the heated zone 714. Where the filament2 has a larger thermal capacity and/or stiffness, the cold feed zone maybegin closer to the heated zone 714 to provide pre-heating of thematerial prior to stitching. Within the cold feed zone 712 (below amelting temperature of the matrix), the filament 2 remains substantiallysolid and rigid, and is maintained in this position until just prior toprinting.

When printing is initiated, the filament 2 is quickly fed and threadedthrough the nozzlet, see FIG. 19D. The cold-feed zone 712 feeds into thelarger cavity heated zone 714, and the filament 2 is constrained fromtouching the walls of the heated zone 714 by the rigidity of theupstream filament still located in the cold feed zone 712, see FIG. 19D.By maintaining a stiffness and preventing melting and wall contact untilthe material has been threaded to the outlet, fibers are prevented frompeeling off, curling and/or clogging within the nozzlet, enabling thefilament 2 to more easily pushed into and through the hot-melt zone 714.In some embodiments, a blast of compressed air may be shot through thenozzlet prior to and/or during threading in order to cool the nozzlet toreduce the chance of sticking to the sides of the nozzle. Additionally,heating of the heated zone 714 of the nozzlet may be reduced oreliminated during a stitching process to also reduce the chance ofsticking to the sides of the nozzle.

As feeding of the continuous core filament 2 continues, the continuouscore filament 2 contacts the build platen 16 or previous layer. Thefilament 2 is then laid or pressed along the surface by motion of thenozzlet relative to the build platen 16. Within a short distance, thefilament 2 contacts the walls of the rounded or chamfered lip 726 nextto the heated zone 714 or nearly contacts the walls of the heating zone714, as illustrated in FIG. 19E. Alternatively, instead of translatingthe printer head, the filament 2 could be driven to a length longer thana length of the nozzlet, and when the outlet is blocked by a previouslayer or by the print bed, the filament buckles to the same effect.After contacting the rounded or chamfered ironing lip 726, the wall ofthe heating zone 714 (or nearly contacting the same), the continuouscore filament 2 is heated to the deposition temperature (e.g., meltingtemperature of the matrix) for fusing the deposited material the buildplaten and/or previous layers. Threading speeds may be between about2500 mm/min and 5000 mm/min.

The rounded or chamfered lip 726 located at a distal end of the nozzletoutlet 716 may provide gradual transition at the nozzlet outlet may helpto avoid fracturing of the continuous core and also applies a downward,compaction, pressing, or ironing force to the continuous core filament 2as it is deposited. That is, “ironing” refers to an act in which (i) asubstantially lateral or transverse force to the side of the filament(e.g., downward if the filament is laid horizontally) is (ii) applied bya smooth surface (partially parallel to the build platen or rounded witha tangent thereof parallel to the build platen) (iii) that is translatedin the printing direction as it presses upon the melted filament tobecome a bonded rank. The rounded or chamfered lip provides a downwardforce, and translates its lower smooth surface parallel to the buildplaten to iron the continuous core filament down to the previous layer.Ironing may be conducted by positioning the lip 726 at a distancerelative to a deposition surface that is less than a diameter of thecontinuous core filament 2; and or by setting the height of a bondedrank to be less than the diameter of the filament 2, but appropriatecompaction force may be achieved without this act (e.g., withsufficiently stiff materials, using the axial compression force only,positioning the lip at a distance greater than the diameter of thefilament 2). This distance from the lip 726 to the previous layer orbuild platen, or the height of a bonded rank may be confirmed using anappropriate sensor.

The ironing and/or axial compression compaction(s) discussed herein donot require a divergent nozzlet. For example, the ironing or ironing lipor tip 726 may be incorporated with a substantially straight nozzlet 720or a slightly convergent nozzlet, see FIG. 20A. Alternatively, or inaddition, a convergent nozzlet may also use a separate cold feed zoneand heated zone, e.g., as shown in FIG. 20B, which shows a convergentnozzlet 728 including a nozzlet inlet 730 that feeds into a cold feedzone 712 which is in fluid communication with a heated zone 714 and thena convergent nozzlet outlet 732.

FIGS. 21A-21D show FFF nozzles which can be employed with the secondary,coating or shell print head described herein according to the presentinvention. FIG. 21A shows a nozzle 800 including an inlet 806 is alignedwith an internal wall 802 that extends up to a convergent section 804and then to a nozzle outlet 808 with an area that is less than an areaof the inlet 806. FIGS. 21B-21D depict various geometries includingsmooth transitions to reduce a back pressure generated within thenozzle. FIG. 21B depicts a nozzle 810 including an inlet 806, aninternal wall 812 with a first diameter initially vertical buttransitioning to a tangential inward curvature 814, and after about 45degrees of curvature, an inflection point 816 reverses curvature andcurves until the internal wall 812 is again vertical, the resultingoutlet 818 aligned with the inlet 810 and with a reduced seconddiameter. FIG. 21C depicts a nozzle 820 with an internal wall thattransitions to a downwards oriented curvature 822 directed towards thenozzle outlet 824. FIG. 21D depicts a nozzle 826 which transitions to achamfered nozzle section 828 which extends up to a point 830 where ittransitions to a downwards oriented curvature 832 to define a nozzleoutlet 834.

FIG. 22 depicts an anti-drip feature for FFF nozzles describe herein. Inthe depicted embodiment, an extrusion nozzle 900 has a material 902 fedpast one or more gaskets 910 and into a cold feed zone 914 and heatedzone 912 prior to exiting nozzle outlet 908. An air channel 904 isconnected to the cold feed zone 914 and is in fluid communication with apneumatic cylinder 906. During operation, the pneumatic cylinder 906 isactuated from a first neutral position to a second position toselectively applying suction to the air channel 904 when printing isstopped. Since the air channel 904 is in fluid communication the coldfeed zone 914 as well as with material within the heated zone 912, thesuction may substantially prevent dripping of polymer melt locatedwithin the heated zone. Once printing resumes, the pneumatic cylinder906 may be returned to the neutral position.

As discussed herein, a “semi-continuous” strand composite has a corethat has been segmented along its length into a plurality of discretestrands. These discrete strands may be a single segmented strand, or aplurality of individual filaments strands bundled together butnonetheless segmented along their length. Discrete segments may bearranged such that they do not overlap. As described herein, thematerial instead of being cut, may be severed by applying a tension tothe material, in most cases while the matrix is melted or softened, andmost usefully at the termination of a printing cycle. The tension may beapplied by either backdriving a feed mechanism of the printer and/ortranslating a printer head relative to a printed part without extrudingmaterial from the nozzle.

FIGS. 23A-24D depict various embodiments of a semi-continuous strandcore filament being deposited from a nozzle, as contrasted to thecontinuous strand core filament 2 depicted in FIG. 24A.

Semi-continuous strands embedded in a corresponding matrix material mayalso have discrete, indexed strand lengths, where termination of thesemi-continuous core occurs at pre-defined intervals along the length ofthe filament (and the strand length may be larger than a length of themelt zone of an associated nozzlet). A semi-continuous strand core mightinclude individual strands or strand bundles arranged in 3-inch (e.g., 2to 5 inch) lengths, cleanly separated such that the fibers from onebundle abut the next bundle but do not extend into the next bundle. Apath planning algorithm controlled by the controller 20 may align breaksin the strand with ends, corners, edges and other stopping points in theprint. Given a printer without a cutter and using indexed strands cannotterminate the printing process until an indexed break in thesemi-continuous strand is aligned with the nozzle outlet, the controller20 optionally fills in areas below the minimum feature length withresin. For example, in many geometries, the outer portion of the crosssection provides more strength than the core. In such cases, the outersection may be printed from semi-continuous strands up until the lastinteger strand will not fit in the printing pattern, at which point theremainder may be left empty, or filled with pure resin.

As depicted in FIG. 23A, a semi-continuous core filament 1000 includinga first strand 1002 and a second strand 1004 located within the matrix1006. The filament 1000 enters a cold feeding zone 712 of a nozzletbelow the glass transition temperature of the matrix. The filament 1000subsequently flows through heated or melt zone 714. The matrix 1006 inthe filament 1000 is melted within the heated zone 714 prior todeposition. Upon exit from the nozzle, filament 1000 is attached to apart or build platen 16 at anchor point 1005. Severance may occur bymoving the print head forward relative to the anchor point 1005, withoutadvancing the semi-continuous core filament 1000; or alternatively theprint head may remain stationary, and the upstream semi-continuous corefilament 1000 is retracted to apply the desired tension. The tensionprovided by the anchor point 1005 permits the remaining portion of thesecond strand 1004 located within the nozzlet to pull the remnant of theembedded strand from the heated nozzle.

FIGS. 23C and 24C shows an indexed semi-continuous core filament 1012where the termination of the core material is substantially complete ateach section, thereby enabling clean severance at an integer distance.The individual sections of core material are separated from adjacentsections of core material at pre-indexed locations 1016. The materialwill exhibit a reduced strength (e.g., compared to bonded ranksincluding embedded fiber) at boundary locations corresponding to thepre-indexed locations 1016 depicted in the figures. FIG. 25 illustratesthe use of such a semi-continuous core filament. As depicted in thefigure, multiple strands 1100 are deposited onto a part or build platen.The strands 1100 are deposited such that they form turns 1102 as well asother features until the print head makes it final pass and severs thematerial at 1104 as described above. Since the individual strands arelonger than the remaining distance on the part, the remaining distance1106 may either be left as a void or filled with a separate materialsuch as a polymer.

While FIG. 23A showed two individual strands, FIGS. 23B and 24B show asemi-continuous core filament 1008 including a distribution of similarlysized strands 1010 embedded in a matrix 1006. While three strands areshown in a staggered line, this is a simplified representation of arandom, or staggered, distribution of strands. For example, material mayinclude about 1,000 strands of carbon fiber (the fiber bundle termed a“lk tow”, although in the present discussion this tow must beappropriately, void-free, embedded in a thermoplastic matrix asdiscussed herein). The strands 214 may be sized and distributed suchthat there are many overlapping strands of substantially similar length.As such, a semi-continuous strand filament may include segments sizedrelative to a melt zone of a printer nozzlet such that the individualstrands may be pulled out of the outlet of the nozzlet. The melt zonecould be at least as long as the strand length of the individual fibersin a pre-preg fiber bundle, or half as long as the strand length of theindividual fibers in a pre-preg fiber bundle. During tensioning of thematerial to separate the filament, the strands embedded in a part oradhered to a printing surface provide an anchoring force to pull out aportion of the strands remaining within the nozzle. For long strands,some strands may be retained within the nozzle, which may result invertically oriented strands, optionally pushed over by the print head,or optionally subsequently deposited layers placed strategically asvertically oriented strands within a material layer.

A material may combine indexed and overlapping strands. For example,indexed continuous strands may be used, in parallel with smaller lengthbundles located at transition points between the longer strands, suchthat the melt zone in the nozzlet includes sufficient distance to dragout the overlapping strands located in the melt zone. The advantage ofthis approach is to reduce the weak point at the boundary between thelonger integer continuous strands. During severance of a given core andmatrix material, it is desirable that the severance force issufficiently low to prevent part distortion, lifting, upstream fiberbreaking, or other deleterious effects. In some cases, strands may bebroken during the extraction, which is acceptable at the terminationpoint. While the strand length can vary based on the application,typical strand lengths may range from about 0.2″ up to 36″ for largescale printing.

FIG. 24D shows an example of a hybrid approach between a semi-continuouscore filament and a continuous core filament. In the depictedembodiment, a material 1018 includes multiple discrete sectionsincluding one or more core segments 1014 embedded within a matrix 1006that are located at pre-indexed locations similar to the embodimentdescribed above in regards to FIGS. 24C and 25C. The material alsoincludes a continuous core 1020 embedded within the matrix 1006extending along a length of material. The continuous core 1020 may besized such that it may be severed by a sufficient tensile force toenable severing of the material at the pre-indexed locations simply bythe application of a sufficient tensile force. Alternatively, any of thevarious cutting methods described above might also be used.

Successive layers of composite may, like traditional lay-up, be laiddown at 0°, 45°, 90°, and other desired angles to provide part strengthin multiple directions and to increase the strength-to-weight ratio. Thecontroller 20 may be controlled to functionality to deposit thereinforcing fibers with an axial alignment in one or more particulardirections and locations. The axial alignment of the reinforcing fibersmay be selected for one or more individual sections within a layer, andmay also be selected for individual layers. For example, as depicted inFIG. 26 a first layer 1200 may have a first reinforcing fiberorientation and a second layer 1202 may have a second reinforcing fiberorientation. Additionally, a first section 1204 within the first layer1200, or any other desired layer, may have a fiber orientation that isdifferent than a second section 1206, or any number of other sections,within the same layer.

FIGS. 27A-27C show a method of additive manufacturing of an anisotropicobject with a printer head 1310. Part 1300 has a vertically orientedsubcomponent 1302 printed with the part oriented with Plane A alignedwith the XY print plane in a first orientation. The printed subcomponent1302 forms a wound conductive coil of a motor, wound around the Zdirection. In order to form another coil on the part 1300, a fixture1304, shown in FIG. 27B, is added to the print area positioned at, orbelow, the print plane 1306. The fixture 1304 holds the part 1300 in asecond orientation, with plane A rotated to plane A′ such that the nextsubcomponent 1308 can be added to the part 1300. The subcomponent 1308is again deposited in the Z direction, but is out of plane withsubcomponent 1302, as shown in FIG. 27C.

FIG. 28A shows the same anisotropic part as FIGS. 27A-27C, but insteadof using fixtures, the printer rotates the part 1300 and the printerhead 1310 about one or more axes. Part 1300 is held in place by arotating axis 1312, which sets and controls the orientation of plane A.In FIG. 28B, rotating axis 1312 has been rotated by 90° to formsubcomponent 1308 in a direction that is perpendicular to subcomponent1302. Conversely, printer head 510 could be pivoted about the XT and/orYT axes to achieve a similar result. Additional degrees of freedom canbe added, e.g., in an automotive application, rotating axis 1312 maycorrespond to a rotisserie, enabling rotation of the vehicle frame aboutthe YT axis to enable continuous fibers to be laid in the X-Y plane, theZ-Y plane, or any plane in between. Alternatively, a fluid rotationfollowing the external contours of the vehicular body might be used tocontinuously deposited material on the vehicle as it is rotated. Such athree dimensional printer might optionally add the XT axis to theprinter head to enable full contour following as well as the productionof both convex and concave unibody structures. In addition or in thealternative to rotating the part 1300 and the printer head 1310, a table1314 supporting the part 1300 could be rotated about the ZT axis toenable spun components of a given fiber direction.

The three-dimensional printer may form three dimensional shells over theouter contour of a stack of two dimensional layers. This may preventdelamination and increase torsional rigidity of the part.

FIG. 29 shows a three dimensional printer head 1310 having thecapabilities described with respect to FIGS. 28A and 28B, used to form apart including a three dimensionally printed shell. The printer head1310 first deposits a series of layers 1320 (which may befiber-reinforced or pure resin, or any combination) to build a part. Theprinter head 1310 is capable of articulating in the traditional XYZdirections, as well as pivoting in the XT, YT and ZT directions.

FIGS. 30A-30C depict various parts formed using the printer headdepicted in FIG. 29. FIG. 30A shows a part including a plurality ofsections 1322 deposited as two dimensional layers in the XY plane.Sections 1324 and 1326 are subsequently deposited in the ZY plane togive the part increased strength in the Z direction. FIG. 30B show arelated method of shell printing, where layers 1328 and 1330 are formedin the XY plane and are overlaid with shells 1332 and 1334 which extendin both the XY and ZY planes. As depicted in the figure, the shells 1332and 1334 may either completely overlap the underlying core formed fromlayers 1328 and 1330, see portion 1336, or one or more of the shells mayonly overly a portion of the underlying core. For example, in portion1338 shell 1332 overlies both layers 1328 and 1330. However, shell 1334does not completely overlap the layer 1328 and creates a steppedconstruction as depicted in the figure. FIG. 30C shows an alternativeembodiment where a support material 1340 is added to raise the partrelative to a build platen, or other supporting surface, such that thepivoting head of the three dimensional printer has clearance between thepart and the supporting surface to enable the deposition of the shell1342 onto the underlying layers 1344 of the part core.

The above described printer head may also be used to form a part withdiscrete subsections including different orientations of a continuouscore reinforced filament. The orientation of the continuous corereinforced filament in one subsection may be substantially in the XYdirection, while the direction in another subsection may be in the XZ orYZ direction.

The inventive printing processes may utilize a fill pattern that useshigh-strength composite material in selected areas and filler material(e.g., less strong composite or pure resin such as nylon) in otherlocations, see FIGS. 30D-30G, which depict stacks of layers in crosssection. A part formed completely from the fill material 1350 isdepicted in FIG. 30D. In FIG. 30E, a composite material 1352 isdeposited at the radially outward most portions of the part andextending inwards for a desired distance to provide a desired increasein stiffness and strength. The remaining portion of the part is formedwith the fill material 1350. A user may extend the use of compositeversus filler either more or less from the various corners of the partas illustrated by the series of figures FIGS. 30D-30G. For example, acontrol algorithm controlled by controller 20 may use a concentric fillpattern that traces the outside corners and wall sections of the part,for a specified number of concentric infill passes, the remainder of thepart may then be filled using a desired fill material.

FIGS. 31A-31C show the cross-section of various embodiments of anexemplary airfoil, solely as one shape that may be formed with differentfiber orientations within various subsections. “Airfoil” herein isinterchangeable with “3D shape having variable strength in differentdirections and along different surfaces”.

FIG. 31A shows a method of building each section of the threedimensional part with plastic deposition in the same plane.Specifically, sections 1350, 1352 and 1354 are all constructed in thesame XY planar orientation. The depicted sections are attached at theadjoining interfaces, the boundary of which is exaggerated forillustration purposes.

In FIG. 31B, part is constructed with separate sections 1362, 1364, and1366 where the fiber orientations 1368 and 1372 of sections 1362 and1366 are orthogonal to the fiber orientation 1370 of section 1364. Byorthogonally orienting the fibers in section 1364 relative to the othersections, the resulting part has a much greater bending strength in theZ direction. Further, by constructing the part in this manner, thedesigner can determine the relative thickness of each section toprescribe the strength along each direction.

FIG. 31C depicts a shell combined with subsections including differentfiber orientations. In this embodiment, sections 1374, 1376, and 1378are deposited in the same direction to form a core, after which a shell1386 is printed in the orthogonal direction. The shell 1386 may be asingle layer or a plurality of layers. Further, the plurality of layersof shell 1386 may include a variety of orientation angles other thanorthogonal to the underlying subsections of the core, depending on thedesign requirements. While this embodiment shows the inner sections withfiber orientations all in the same direction 1380, 1382, and 1384, itshould be obvious that subsections 1374, 1376, and 1378 may be providedwith different fiber orientations similar to FIG. 31B as well.

FIG. 32 depicts an optional embodiment of a three dimensional printerwith selectable printer heads. In the depicted embodiment, a print arm1400 is capable of attaching to printer head 1402 at universalconnection 1404. An appropriate consumable material 1406, such as acontinuous core reinforced filament, may already be fed into the printerhead 1402, or it may be fed into the printer after it is attached to theprinter 1400. When another print material is desired, print arm 1400returns printer head 1402 to an associated holder. Subsequently, theprinter 1400 may pick up printer head 1408 or 1410 which are capable ofprinting consumable materials that are either different in size and/orinclude different materials to provide different.

Although one version of the invention uses thermoplastic matrix, hybridsystems are possible. A reinforced filament may employ a matrix that isfinished by curing cycle, e.g., using heat, light, lasers, and/orradiation. For example, continuous carbon fibers are embedded in apartially cured epoxy such that the extruded component sticks together,but requires a post-cure to fully harden. Similarly, while one versionof the invention uses of preformed continuous core reinforced filaments,in some embodiments, the continuous core reinforced filament may beformed by combining a resin matrix and a solid continuous core in theheated extrusion nozzle. The resin matrix and the solid continuous coreare able to be combined without the formation of voids along theinterface due to the ease with which the resin wets the continuousperimeter of the solid core as compared to the multiple interfaces in amultifilament core. Therefore, such an embodiment may be of particularuse where it is desirable to alter the properties of the depositedmaterial.

FIG. 33 depicts a hybrid multi-element printer head 1500 that is capableof selectively extruding material feed options fiber or wire 1502, firstmatrix 1504, and second matrix 1506 as well as an optional cutter 8.More specifically, the multi-element printer head 1500 is capable ofselectively depositing any of material feed options 1502, 1504, and1506, as singular elements or in combination. For example, material 1502is a continuous copper wire fed through a central channel; material 1504is a binding resin such as Nylon plastic; and material 1506 is adifferent binding resin such as a dissolvable or soluble supportmaterial. The printer head 1500 extrudes all the elements at once where,for example, the copper wire 1502 surrounded by the nylon binder 1504 onthe bottom surface and the dissolvable support material 1506 on the topsurface, see section 1508. The printer head 1500 may also deposit thecopper wire 1502 coated with either the nylon binder 1504 or the solublesupport material 1506 separately, see sections 1510 and 1514.Alternatively, the multi-element printer head 1500 may deposit the abovenoted material options singly for any number of purposes, see the barecopper wire at section 1512.

The printer head 1500 optionally includes an air nozzlet 1508 whichenables pre-heating of the print area and/or rapid cooling of theextruded material, see FIG. 33. The air nozzlet 1508 may enable theformation of structures such as flying leads, gap bridging, andunsupported features. For example, a conductive core material may beextruded by the multi-element printer head 1500 with a co-extrudedinsulating plastic, to form a trace in the printed part. The end of thetrace may then be terminated as a flying lead or pigtail. To achievethis, the multi-element printer head would lift, while commensuratelyextruding the conductive core and insulating jacket. The multi-elementprinter head may also optionally cool the insulating jacket with the airnozzlet 1508. The end of the wire could then be printed as a “strippedwire” where the conductive core is extruded without the insulatingjacket. The cutter 8 may then terminate the conductive core. Formationof a flying lead in the above-noted manner may be used to eliminate astripping step down stream during assembly.

FIG. 34 depicts a different hybrid system, employing stereolithography(and/or selective laser sintering) to provide the matrix about theembedded fiber, i.e. processes in which a continuous resin in liquid orpowder form is solidified layer by layer by sweeping a focused radiationcuring beam (laser, UV) in desired layer configurations. In order toprovide increased strength as well as the functionalities associatedwith different types of continuous core filaments including both solidand multifilament materials, the stereolithography process associatedwith the deposition of each layer can be modified into a two-stepprocess that enables construction of composite components includingcontinuous core filaments in desired locations and directions. Acontinuous core or fiber may be deposited in a desired location anddirection within a layer to be printed, either completely or partiallysubmerged in the resin. After the continuous fiber is deposited in thedesired location and direction, the adjoining resin is cured to hardenaround the fiber. This may either be done as the continuous fiber isdeposited, or it may be done after the continuous fiber has beendeposited. In one embodiment, the entire layer is printed with a singlecontinuous fiber without the need to cut the continuous fiber. In otherembodiments, reinforcing fibers may be provided in different sections ofthe printed layer with different orientations. In order to facilitatedepositing the continuous fiber in multiple locations and directions,the continuous fiber may be terminated using a cutter as describedherein, or by the laser that is used to harden the resin.

FIG. 34 depicts a part 1600 being built on a platen 1602 usingstereolithography. The part 1600 is immersed in a liquid resin(photopolymer) material 1604 contained in a tray 1606. During formationof the part 1600, the platen 1602 is moved by a layer thickness tosequentially lower after the formation of each layer to keep the part1600 submerged. During the formation of each layer, a continuous corefilament 1608 is fed through a nozzlet 1610 and deposited onto the part1600. The nozzlet 1610 is controlled to deposit the continuous corefilament 1608 in a desired location as well as a desired directionwithin the layer being formed. The feed rate of the continuous corefilament 1608 may be equal to the speed of the nozzlet 1610 to avoiddisturbing the already deposited continuous core filaments. As thecontinuous core filament 1608 is deposited, appropriate electromagneticradiation (e.g., laser 1612) cures the resin surrounding the continuouscore filament 1608 in a location 1614 behind the path of travel of thenozzlet 1610. The distance between the location 1614 and the nozzlet1610 may be selected to allow the continuous core filament to becompletely submerged within the liquid resin prior to curing. The laseris generated by a source 1616 and is directed by a controllable mirror1618. The three dimensional printer also includes a cutter 1620 toenable the termination of the continuous core filament as noted above.

Optionally, the deposited filament is held in place by one or more“tacks”, which are a sufficient amount of hardened resin material thatholds the continuous core filament in position while additional corematerial is deposited. As depicted in FIG. 35, the continuous corefilament 1608 is tacked in place at multiple discrete points 1622 by thelaser 1612 as the continuous core filament is deposited by a nozzle, notdepicted. After depositing a portion, or all, of the continuous corefilament 1608, the laser 1612 is directed along a predetermined patternto cure the liquid resin material 1604 and form the current layer.Similar to the above system, appropriate electromagnetic radiation(e.g., laser 1612), is generated by a source 1616 and directed by acontrollable mirror 1618. The balance of the material can be cured tomaximize cross linking between adjacent strands is maximized, e.g., whena sufficient number of strands has been deposited onto a layer andtacked in place, the resin may be cured in beads that are perpendicularto the direction of the deposited strands of continuous core filament.Curing the resin in a direction perpendicular to the deposited strandsmay provide increased bonding between adjacent strands to improve thepart strength in a direction perpendicular to the direction of thedeposited strands of continuous core filament. If separate portions ofthe layer include strands of continuous core filament oriented indifferent directions, the cure pattern may include lines that areperpendicular or parallel to the direction of the strands of continuousfibers core material in each portion of the layer.

To avoid the formation of voids along the interface between thecontinuous core filament and the resin matrix during thestereolithography process, it may be desirable to facilitate wetting orwicking. Wetting of the continuous fiber and wicking of the resinbetween the into the cross-section of the continuous multifilament coremay be facilitated by maintaining the liquid resin material at anelevated temperature, for a certain amount of time, using a wettingagent on the continuous fiber, applying a vacuum to the system, or anyother appropriate method.

In addition to using the continuous core reinforced filaments to formvarious composite structures with properties in desired directions usingthe fiber orientation, in some embodiments it is desirable to provideadditional strength in directions other than the fiber direction. Forexample, the continuous core reinforced filaments might includeadditional composite materials to enhance the overall strength of thematerial or a strength of the material in a direction other than thedirection of the fiber core. For example, carbon fiber core material mayinclude substantially perpendicularly loaded carbon nanotubes. Loadingsubstantially perpendicular small fiber members on the core increasesthe shear strength of the composite, and advantageously increases thestrength of the resulting part in a direction substantiallyperpendicular to the fiber direction. Such an embodiment may help toreduce the propensity of a part to delaminate along a given layer.

1.-20. (canceled)
 21. A method for additive manufacturing, the methodcomprising steps of: threading an end of a filament through a channel ofa printhead to an outlet, the filament comprising a substantiallycontinuous fiber core extending within a matrix material, and threadingincluding feeding the filament in an unmelted state; maintaining astiffness of the filament, including passing the filament through a coldfeed zone having a temperature that is below the melting temperature ofmatrix material; and heating the filament at a temperature greater thana melting temperature of the matrix material in a transverse pressurezone at the outlet.
 22. The method of claim 21, wherein the temperatureof the cold feed zone is below the glass transition temperature of thematrix.
 23. The method of claim 21, wherein the substantially continuousfiber comprises a sectioned continuous core.
 24. The method of claim 21,wherein the step of maintaining a stiffness comprises preventing wallcontact of the filament until it has been threaded to the outlet of theprinthead.
 25. The method of claim 21, wherein feeding comprises pushingthe filament in an unmelted state.
 26. The method of claim 25, whereinwhen pushed the unmelted filament is sufficiently stiff to preventbuckling.
 27. The method of claim 25, wherein when pushed the unmeltedfilament is sufficiently stiff to prevent peeling off.
 28. The method ofclaim 25, wherein when pushed the unmelted filament is sufficientlystiff to prevent curling.
 29. The method of claim 21, wherein the matrixmaterial is characterized in that it exhibits no appreciable tack inambient conditions.
 30. The method of claim 21, wherein prior to thestep of threading is a step of cutting the filament.
 31. The method ofclaim 21, wherein prior to the step of threading is a step of runningout the filament.
 32. The method of claim 21, wherein prior to the stepof threading is a step of separating the filament.
 33. The method ofclaim 21, wherein the step of maintaining further comprises feeding thefilament through a heated zone having a cavity that is larger than thatof the cold feed zone.
 34. The method of claim 33, wherein the cavity ofthe heated zone has a larger diameter than that of the cold feed zone.35. The method of claim 33, wherein the heated zone diverges to a lip atthe outlet.
 36. The method of claim 21, further comprising a step ofpre-heating the filament through a hot melt zone between the cold feedzone and the transverse pressure zone.
 37. The method of claim 21,wherein the step of heating the filament at a temperature greater thanthe melting temperature of the matrix material in the transversepressure zone melts the matrix material interstitially within one ormore fibers within the filament.
 38. The method of claim 21, furthercomprising a step of applying an ironing force to the filament with alip.
 39. The method of claim 21, further comprising a step of applying atranslating force to the filament with the lip.
 40. The method of claim39, wherein the translating force comprises a tension on a part and/or asurface.
 41. The method of claim 21, wherein the transverse pressurezone is a print head tip.
 42. The method of claim 21, wherein thetransverse pressure zone is an ironing lip.